Not illegal, no requirement for back windows in the UK. Well, certainly not for vans.
But it's the first vehicle I've had without back windows, so I'm now looking into a rear camera linked to a rear view mirror screen.
The plan at the moment is to use some sort of insulation in the cavities (behind side wall ply), then bubble insulation it (like below), then carpet line. But will possibly make use of the ply somehow. Certainly want a solid base, but don't necessarily need the ply on the sides.
Carpet lining something like this - but maybe not the floor.
