I would DIY, starting with the living space "pod", as light as possible, so only as strong as truly necessary.
Aluminum profile frame, strongest part the bottom perimeter and cross-beams, make sure perfectly 90° / parallel.
Foamie style PMF top & sides, rather than fiberglass
no metal above floor level, unless you need a roof rack e.g. for solar.
Floor using poly greenhouse benchtop flats, add a continuous sheet of foam insulation below if needed, can also spray infill, skinned inside with luan 1/8" underneath with aluminum skin
High-tech adhesives use everywhere possible for lightweight strength, more so than fasteners.
Load it up once finished if any: propane, batteries, toilet, fridge, stereo, water & grey/black tanks food clothes tools etc etc
plus mammal(s) of course.
Only then look at the wheels/axle/suspension, lightest weight, sized for the above total **only** and no more.
Actually plus hitch tube frame of course, added last of all.
If the hitch + axle can be an integrated platform, supporting the "living pod" but detachable, that gives a lot of flexibility and a bit of extra strength.

> plastic sheets with air pockets
forget those, whatever you mean