Advice on building a non warping board?

Hi guys

A friend is planning to build a two tier layout for his Scalextric track and railway layout. Each will be on a separate board approx 7 ft square. To make best use of available space (and to secure domestic approval!!!!!) the layouts have to be movable. In use, they will sit across a couple of single beds. When not in use they will be stacked on edge against a wall. The Scalextric will probably be the bottem board, with 6-7 in spacer blocks built in to allow the other board on top when he wants to use the train set. Obviously, both tracks will need to be fixed down to allow the boards to be tipped upright, and buildings/scenery will either have to be low level or removable. Why this approach? The ceilings are quite low, so there isn't room for a fold down type layout, and the room is built into a dormer roof, so a winch down layout is impractical. The boards have to be stackable, as there isn't enough room get one out of the way when you want to use the other.

Sooooooooooo...........

What we need is then to build two 7 ft square decks, that are solid enough to withstand being moved from vertical to horizontal, rigid enough not to flex or warp, and light enough to be moved.

My initial thoughts are to have a 2"x1" timber frame (with bars every 12"?) skinned with 6mm MDF top and bottem. I'd add triangular corner blocks inside the frame to increase strength. The hollow design allows wiring to be concealed. Alternatively the frame could be done in aluminium (at much greater cost....)

Has anyone out there ever attempted anything like this? Anyone got any thoughts?