[jbjburbs]

not a pro but...most under seat boxes are made slimmer, but not smaller in size. people (and companies) add space by making the boxes longer/wider than they would a typical box. my basic understanding is that to get decent sound the sub needs a certain amount of cubic space (from the box). if the sub is short enough to fit under the seat you could make a box twice long to fill the space under the seat. to be technical you could probablly find the amount space recommended for your sub and build accordingly..