Originally Posted by kaput

My brother built a custom shaped box in his 2006 Rabbit. We replaced the under the floor styrofoam panels with a wood box, the same height and installed a pair of Kicker 8" woofers.

I know it is not 100% true, but 2 8" woofers = 1 12" woofer. It is powered by a 500 watt mono block amp and can thud when needed. We are musicians, so we are all about SQ. He is running focal 3 ways in the doors, Sony Mobile ES separates in the rear and the 2 kickers for bass. The system sounds immense and clean... Like, really clear and tight.

We did analyze the system with a flat response room mic, and made adjustments using his old Audiocontrol EQS to make it as flat as possible.

All I am saying is, you can use 2 8" subs in a box made for them (sealed and separated) and still make bass. Funny enough, without the subs, the locals still play stupid low and loud, like 40hz loud. They still need help, but can do without them.

If it were me, I would go the small approach. The box will be lighter, and easier to remove if needed, but will be under the floor, so you have the cargo area. Install the amp in the same cavity, but not on the box, so you can remove the box if needed. Then again, you can always go for bigger if you think it is better. I personally love bass to be tight and accurate.