actually, when i made this i only thought of using styrofoam, but i realised later when i tried putting my figures its a headache. cause the racks are supported by two stands, about 1/3 from the sides, the weight of figures is actually enough to bend the 1cm thick layer of styrofoam. further more i didnt glue them onto the stands, if i place one figure on one side, i must have another on the other side to counter-balance
i've got one suggestion but i didnt try it though, but coroplasts are a good idea. I think by putting two layers of coroplasts perpendicularly on each other, they make a good supporting platform, just like plywood works by having different layers of wood glued perpendicularly.
coroplast