Me and my friend lee build a dual 12" sub enclosure to slip behind the seat of my K30, and if anyone wants the dimensions I'd be happy to give them.
What suprising is that considering the kinda shoddy contruction, the box holds together well and we've gotten really good bass out of the two Pyle Blue Waves we've mounted in it (when hooked to an Alpine V12 MRV-1505 amp).