I don't see any reason why putting a 2X4 in the box would hurt anything, and would make the volume smaller. One thing is just make sure that it is attached nicely to the box, don't want that superglue and tape to break loose

2002 Ford ZX2 5spd (2nd baby) Former owner of 1998 Mystique (never filled the shoes on my first love)parents traded for new sable Former owner of 1996 Mystique(My true baby )