one method to gain clearance, is to cut a hole in the back of the baox and install a metal plate. i actually have a stack of aluminum plates for this purpose, and they can transfer heat. alternatives will depend on price, but have you given thought to deflection clearance? you have to think about cone rigidity and box space. infinity perfects are a nice choice, and have a tuneable pole vent, but are kind of sensitive to heat near max power. also look at eclipse, kicker, and phoenix gold. the kicker l-series fairs well in trucks, since you can get the same output with a smaller sub. regarding shallows- they are making large improvememnts lately in shallows, and it would also allow you to move the sub further away from the deflection source. i am assuming the sub fires at the floor..... also, i have seen a real nice design for a slotted vent box that fires square 8's foreward, but still all contained under the seat. 2 8's can get you 125db+ @5-600wrms easily
