are you talking about a true false floor? that wouldn't exactly leave your car streetable. if this were the case you wouldn't be asking these questions, cause the car obviously wouldn't be your daily driver, so i'll move on to...
or are you talking about something just to cover the hatch area? that isn't really a "false floor" i could go into more detail, but don't feel like typing it all. if you just wanna cover the hatch, then your best bet is to just build a sub box, and use another piece of MDF, plywood, fiberglass, whatever and make a "cover" for it all just going over the top, and you can flush mount whatever into that
