I have to make four stage blocks (rostrum blocks) for our theatre group. They have to be easy to erect and dismantle. I'm thinking of 4'x4' blocks 2' high which will be easy to cut from sheet materials. Four sides held together with theatrical backflap hinges and a top that drops on but located by corner blocks. 16mm ply seems to be the obvious material to use but I'm prepared to be guided to other products. Would I need to have a midrib to support the 4'x4' platform? It would have to carry 2 - 3 adults.