I am wanting to make a trench run board (with a 3D trench) to run a game at a local convention coming up. However, I would like to make it so it breaks down in to flat pieces, yet it stiff enough to stand up to play. I prefer foam core as a base with paper surface glued on as that is the easiest material for me to work with.

My current idea is to make the trench with mitred corners that act like hinges. I would then pin them with sewing pins for play. Anyone have any better ideas?