Last time I made box in any size with single layer acrylic. But it will fall apart if you don't use glue. I want the box module pieces can be reused, so glue is not a good solution. I looked for some connection of flat pieces like wood floor and clamp.
Then I made this 3 layers module with two types of connectors, flat and rect.
Good news is it can support some weight now, bad news is not much weight.