My best direction would be to put an aluminum floor in with screws. That way you can take it out and check, or replace your foam when the time comes. I wouldn't put plywood in it if I planned on fishing it a lot, or it being out in the weather very much. If you are not out in the weather, and keep it covered otherwise, 1/2" plywood over foam would probably be the minimum I would do. I like the aluminum though.