I'm curious to know if one must line the bottom and sides of the box with plywood as well as the top of the box?
I would think (yes.) Most powder cabinets or chests that I've seen were made almost entirely out of wood with a lock hasp on there door or lid. I'm pretty sure the idea behind a powder cabinet was not
to contain a explosion if one were to take place. A chest or cabinet being made of wood, plywood, chipboard, definitely helps to control static electricity too.