I built a one-man caravan cum load carrier last year using a 110 roof for the roof and wood and palstic sheeting for the sides. I built an elevating system out of two builders trestles attached to the front and rear so I can lift the roof from driving height to standing height. (I am 1.8 metres tall so the roof is at least that high when lifted)
There is a porta poti and butane powered cooker and heater run from disposable canisters, with water and power from a car battery and inverter with solar charger on board.
Having used it for a year, I am now designing a replacement module made from two cut up brownchurch roofracks, one forming the base and one attached to the roof inverted so I dont have to fabricate a frame, just weld up bracing beams between them.
I initially inverted the tow ring and damper to drop the height of the trailer hitch and put on 14 inch Land rover pattern wheels to level it out. I toyed with the idea of extending the A-Frame to reduce jack-knifing, but eventually built an extension beam from square profile stainless tubing and bolted it on to the A-Frame. Cut outs allowed the damper assembly to be put on the end of the extension bar inverted so the trailer rides level and balanced.
I took off the military swing down jockey wheel mount to reduce weight, and replaced it with a standard jockey wheel mount bracket.
I have a 25 litre water tank and 25 litre fuel tank strapped to side steps at the rear and the spare wheel mount is bolted to the centre of the side panel over the wheel to maintain balance.
I can move the trailer on a flat track alone and the military pintle I bought from Ebay for £30 is the dogs whatsit.
I have a leather sofa and a pop up ambulance trolley for a bed inside so it functions like a caravan, and 12volt lighting inside and out so it is a good base for isolated pitches. I have installed a carbon monoxide alarm for when I use the cooker and heater inside, although the fans and vents I built in to the floor and roof reduce the risk of build-up in use.
All together the whole trailer cost £300 including the purchase of the trailer chassis from Witham, the MOD sales people. I bought it without the tub because I would have had to remove it anyway.
Having used it for a year for metal detecting rallies and holidays in snowdonia national park, it is time for a revamp and airodynamic styling to cut down on fuel costs when towing.
Good luck with your trailer, it looks like a proper job.
Eric