12" sub? Man, how you gonna get that back there? I'm designing the boxes for my 6-1/2's and I'm gonna lose about an inch of seat travel to make room.
Why do you need a 12" sub in a car that small? I mean, I find it difficult rationalizing my two 6-1/2's (except that only using one would make things uneven LOL). Anyway, you might want to save yourself some frustration and consider going a bit smaller. Check out Elemental Designs (
Elemental Designs). They have some killer subs that are pretty compact and some don't even need to be boxed. Frequent sales, too.