I have seen pictures of an 88mm gun being loaded, &, I think, the 8 wheel armoured car
(Puma). The interior of the doors is mostly bracing struts, & half round formers, rather like hoops to form the curve of the the skin which seemed to be fabric.
I can't remember where I saw it all though. The flaps would be manual, probably on some sort of pulley system, maybe even wound down. So once they're down, they may as well stay down for the next take off. Thats going to be a big diorama, how big are the shelves in your house?
Hope this helps.
Pete