In most, we do them behind the rear seat. If you have a power slider, you may want to look at the JL Audio center console stealthbox. There are still bass solutions (like ported 8") behind the seat but the window motor is in the way of a large enclosure.
Thanks EW! I do not have a sliding rear window. I also wasnt sure if I would have to use the slim line sub's because of the limited space back there. Would this be a custom box or something that can be picked up say at your place or online?
I'm sure that there are premade enclosures that fit but the ones we usually see mash the woofer against the back of the seat which is not good. JL 10W1v2 woofers will fit without having to resort to a thin woofer. Some 8" drivers would probably fit well too. 3-10" or 4-8" would sound good. Plenty of options but I would use a custom enclosure.