What is described below more resembles a camping trailer but it is a true caravan since all accommodation and facilities are contained within without resorting to any fold out or canvas sections (except for the pop top roof).

The aim is to be totally independent and self supporting in isolated areas for at least a week.

The design criteria are as follows...

*	Sleeping accommodation for two.
*	Absolute minimum frontal area.  Maximum towing height including solar panel must be less than 2.1M.  (Want to negotiate height barriers in car parks etc.)
*	ATM (mass loaded) not to exceed 1000 Kg (750 Kg for the trailer slideon camper.)
*	Seating for two.
*	Must have s/s sink and 2 burner stove with grill (Maxie or Origo metho (alcohol) type - we are ex-boaties).
*	Must have  50 Lit compressor fridge.
*	Must have adequate on board storage for battery, inverter, generator and outside fold up table and chairs.
*	Minimum 70 lit water tank.
*	Must have a small enclosed loo.
*	80W minimum solar panel on roof.

I have been thinking about this for quite some time and in the last couple of years I have been doodling various designs with the aid of 2D cad software that I have been using for years.

It started off as a slideon camper for our 7'x4' galvanised box trailer and soon turned into a stand alone little caravan 2.5M x 1.7M.    The reason being, I just wasn't satisfied that everything on my "must have" list was fitting satisfactorily into the slideon.

My slideon design used a full size front hinged pop-top whereas the little caravan had a smaller full lifting pop-top.    Both used bunk beds, one above the other and a rear door, this is the only way I could see to keep the width down while incorporating all the features we wanted.

As it turns out, the toilet compartment is almost as large as the shower/toilet in our Golf Bushman (although head room is restricted) and the front storage area volume is similar.

Beds are 1900 x 650mm each.
Wardrobe / drawers W=480mm x D=600mm x H=1400mm
Bench space with sink & stove 1200mm x 470mm
Head room with roof up 1.6 M lowest to 2.1 M highest at the rear.

The overall length of the camper excluding the draw bar, front storage box and spare tyre is 2.45 M.

It's surprising what you can comfortably fit in a small space by reclaiming the floor space of one bed.

There is ample seating for two, the top bunk hinges down to become the backrest for the bottom bunk along the left side of the camper.  Also on the left side at the rear is the wardrobe.
On the right hand side at the rear is a stove with fridge underneath and a next to that is sink with a cupboard underneath.  At the rear is an enclosed toilet and hand basin.
Underneath the lower bunk is stowage for the annex and outside table and chairs and a sealed 12V battery forward.

Initial calculations indicate an unladen mass of 820 Kg so I would have to refine the design a little to keep the laden mass below the target 1000 Kg.

Then just recently, mainly due to the use of some new 3D modeling software, I have come a full circle in both design and construction method.

I modeled both of my concepts, the stand alone mini caravan and the trailer mounted caravan/camper.
In a "walk through" of both the virtual caravan and camper I was convinced that this concept and layout would be quite practical and would fulfill all my criteria even better than I had expected. 

After two years of contemplating and doodling I am now thinking that my original slide-on concept is going to be quite adequate for our needs, quite a bit simpler and cheaper to build with no annual rego to worry about.
There was so little difference between the two that I have opted for the trailer mounted caravan/camper.

The only significant difference is the camper sits on a 7' x 4'  box trailer, is 250Kg lighter, has a full pop top and a smaller water storage capability of 85 litres.
This interior design and layout is virtually identical in that it still has two bunk beds, an enclosed loo, a bench top for sink and stove and a 50 litre Waeco fridge/freezer.

 

The illustration on the left gives an idea of my 2nd generation mini caravan design with an ATM (all up mass) calculated to be 1000Kg. I persevered with this design for quite some time until the advent of some 3D modeling software that convinced me that the trailer slideon was just as "roomy" and far easier and cheaper to build and own. In my 08 rewrite of this page, I have deleted most of the info pertaining to this version but even though concept and construction are different, layout is all but identical to the current slideon version.

The advantage of this slide-on over the mini caravan - simpler construction, lighter, no engineering certificates needed and no additional annual registration fees.

Originally the idea was that it should be suitable for frequent shorter duration trips, we were looking at trips up to a week duration and into areas not suitable for full sized caravans.
Now we are hoping it will be a replacement for our Golf Bushman where we do trips ranging from a couple of weeks to a couple of months especially when used with the annex described below.


The slideon camper offers better accommodation than a typical HiAce / VW size campervan and the tow vehicle & camper combination has considerably better off road ability and much better driver/passenger collision safety than the typical forward control van conversions. 

This one would slide on to our galvanised  2100 x 1200 mm (7' x 4') box trailer.
The trailer has an unladen mass of 250 Kg including a spare tyre and maximum loaded 750Kg, the legal limit for an unbraked trailer.

The overall length of the camper (excluding draw bar) is 2.44 M, width is 1.68 M and height is 2.0 M and with the pop top up is 2.5 M.
Interior headroom is 1.5 M with the roof down to >1.9 M over the standing area with the roof up.

Suspension is the usual leaf sprung beam axle and 195R14LT tyres rated at 960Kg each.

I know an all up mass of 750 Kg is a lot for something so small compared to a commercially built caravan but I want this to be very rugged to reliably go almost anywhere the 4x4 can.

It is not intended to be hard core bush bashing camper, even your average well built box trailers are just not suitable for that kind of punishment without extensive modifications, but it will enable us to venture into areas out of reach of most caravans.
Even now we can venture into almost all camping areas we choose with our Golf Bushman, this one would enable us to go even further.

I have two options for the construction.
Either it could be constructed of aluminium square tube (not "C" section like most caravans) with aluminium exterior and plywood interior.
Or, far simpler to build, 10mm marine plywood lower section and 6mm marine ply with 0.8mm prepainted stucco aluminium outer skin bonded directly to the ply top sides with no framing, relying on the interior furniture as structural elements.
The roof in both cases would be an aluminium/3mm ply/HD foam/3mm ply laminate.
After a lot of thought, I have opted for the aluminium frame construction, mainly so that I could more easily insulate the camper, in this case with 25mm of polystyrene foam.

The trailer would undergo a couple of minor modifications, lengthened and strengthened "A" frame and replacement of the ball coupling with a Tregg or preferably  Orac type, as shown on the left, to give the degree of articulation needed for more difficult terrain.
 
Something this small can't be made to look streamlined and stylish so I am quite happy to make it look like a camping trailer without trying at all to make it look like a caravan hence, by necessity, the simple to build space efficient boxy shape.  

I am struggling to get down to my target of 500 Kg for the loaded slide-on by the time I included water, battery, solar panel, fridge, generator, annex, toilet and personal effects etc. whilst maintaining desired strength.
 If I do exceed the magic 750 Kg all up, it means fitting brakes to the trailer (which I probably would do anyway if this project proved to be as successful as I hoped).

A couple of you emailed me suggesting moulded fibreglass but I prefer aluminium and plywood for a number of reasons, not the least of which is ease of construction for a one-off project.     To use moulded fibreglass, you need a mould and to get the mould you must first build a "plug" and the end result would be double the weight or ten times the cost if the weight and strength were the same as the marine ply or aluminium framed construction.

The screened door, windows and 85 lit water tank are all stock off the shelf items.

I tried dozens of variations in the front to try to give it a more streamlined appearance but none looked quite right so I will stick with the basic box shape.   In any case, I don't think any variations of the frontal area that would be practical will cause much if any reduction in drag since it is almost completely in the slipstream of the tow vehicle.

The accommodation, while certainly not palatial, would be quite adequate for us.

The table at the end of this page is a comparison of the calculated performance of our present Golf Bushman and the proposed mini van and slide-on.

Based on those figures I would be hoping for 8.5 to 9.0 Km/Lit, up from the present 6.0 to 6.5 Km/Lit, a significant reduction in fuel consumption in the order of better than 40%.    Wind resistance due to frontal area is the main enemy.

The advantage of this type of pop top roof compared to a fully elevating pop top is ease of use and better strength to weight ratio.  The biggest disadvantage of this type of pop-top roof is the solar panel angle, OK if I always park facing north.  May have to either hinge the panel or relocate it.


Clearly this type and size caravan/camper isn't for everyone, but for us, it's advantages should weigh it's disadvantages.


Loading and unloading the camper from the trailer.

To load and unload the camper from the trailer shouldn't be too difficult.
The principle here is based on the fact that as you raise and lower the front of the trailer with the jockey wheel, the body of the trailer will pivot about the axle.   A weight bias ahead of the axle is assumed and of course, stable towing would mandate this in any case.

Imagine the slideon camper in position on the trailer, now wind the jockey wheel so the front is lowered and the rear, conversely, is raised.
Now fit two (removable) legs at the rear of the slideon of such a length that they contact the ground.
Now wind the jockey wheel so as to now raise the front, the rear of the trailer will drop leaving the rear of the slideon supported only on the removable legs (and the front still on the front of the trailer).
Now place two more removable legs at the now raised front of the slideon and then level the trailer. 
The slideon should now be supported solely by the four legs at a height above the trailer determined by the range of movement of the jockey wheel.
(25mm of clearance would be ideal and easily obtainable, much more and you would have to start thinking about slightly reducing the floor length of the camper inside the trailer to avoid the problem of trailer & front of camper contact when loading/unloading.)

Loading is the reverse.

In practice, the legs would need to be "L" shape such that the (front) legs are sufficiently clear the trailer wheel guards to allow extricating the trailer.
Some 35x35x2mm steel should be adequate for the four legs (they are only around 500mm long x 300mm to form the "L").  Permanent sockets with 35x35mm id could be fitted under the "wings" to receive the legs.    At around 5.5Kg total, it would be feasibly to carry these legs in case needed while you are away.

An advantage of this method is that you are only lifting the front of the slideon and that is with the aid of the jockey wheel so the whole operation shouldn't require much effort.     That's my theory anyhow.    If I'm wrong I'm sure someone will let me know.

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We found very early in our caravanning that an outside awning of some description with at least one wall, preferably two, is essential and even more so with this tiny caravan. The intention would be to use the Oztent model RV-3 as an annex to give some more living space on anything longer than an overnight stop as shown in the graphic on the right. We envision purchasing the optional side walls to enclose the awning as well, giving quiet a roomy living space when needed (which I have not shown).

Photo and animation  from Oztent web site  http://www.oztent.com.au/