Ok so far I've got this:
The rear will kind of look like this:
The trailor will be be made of a light timber frame, plywood sheets then fiberglass/epoxy/gelcoat so it will be lightweight but strong. However, my carpentry skills are not great so the edges will be 90°, as in not radii(?) or rounded. EG, The sides and top will have the correct curvature to 18° or however far I can go within 3.5/4 metres limitation, but where each side meet will be 90° joints. How big an effect will this have?
OK, I got Sketchup and had a play with it, I don't understand how to do curves, but here is my trailer idea with straight panels, but basically the same.
