make a panel that covers the whole floor out of 1\2" or something, and then make a raised up platform for the usamps and cut a hole in the top to see the top of the amp and put some plexi in there or just let the top of the amp stick thru level with the top of the board.
make sure the platform under the usamps is level and makes the amp raise up to the top of the 1\2" board.
easy.