it moves all over the place, plywood or not. The screws tend not to come undone really but they do need re-tightening because the wood shifts.

I closed the openings on mine with polycarbonate. When it is cold you can remove the polycarb but when it is hot you can't, it is absolutely stuck tight, it will break rather than come out so the printer size must vary enormously between hot and cold. I think I'll measure it to see how much it changes, certainly the hole gets at least 1.5mm smaller or the polycarb gets 1.5 mm bigger when it is hot.