Drew out the plans for my new sub (on the way in the mail). Subs a polk MM1040, box is about .67 cubic feet. The box is going under my left rear passenger seat in my sierra. External dimensions are 18" wide, 7"deep, 14"long at the top and 12" long at the bottom, Building out of 3/4 in mdf. Only issue i might see is that the sub is only going to be about an inch to two inches from the bottom of the seat, is this going to cause any disruptions in sound? I figure I will just fold the seat up when theres 2 people in my truck.