Even with a sub only 7 inches deep its going to be tough to fit it under a jump seat. theres just under 10 inches from the metal floor board to the bottom of the seat. the padding and vinyl/carpet is about an inch and a half. so you have about an inch and a half to play with. I did it with 2 10 inch subs. This was 2 years ago so my numbers may be wrong, these measurments are all by memory. Mine didnt turn out so well. Lucky I very rarely had any passengers in the back.
The passenger side box is the one I did, the seat just barely came to the top of the box. I resessed the sub about an inch, thats why mine was so tight, but the sub didnt bump the bottom of the seat.
I ended up just sacrificing one jump seat. I liked this set up a lot better.