Come on, it can't be that hard to figure it out. if you haven't got the technical knowledge to figure out how to put a hinge on a drop in, maybe you shouldn't build one. The hinge will severely weaken your design, I think your best off with the usual, unless there is absolutely no way at all to take it with you.
what you could do, is make two triangles of sorts, with sides that all have hinges, except one corner. On that corner, have a simple lock mechanism, as in a peg-and-hole setup. Put plywood between them, voila you have the drop. for the flat part on top, just use some milk crates or another triangle set up a small distance away, with some plywood on top.
Etch-a-sketch, but I don't see why it wouldn't work.