Hi all, I am new to the site but if I may offer my little bit, reads90 got it right, keep it simple and make it strong.
The more you build in the heavier it will get. You need a strong chass single axle, and strong axle set up with shocks. Stub axles have a tendancy to part from the trailer. Beefed up caravans will not hack it, they disintergrate on the move. The more you keep it simple and max storage the more versitle it will be. Best base is an ex army trailer 3/4 or 1 ton. build your own it will be half the price.