Heres the link to the JL site for that stealth box,
JL Audio: Products . Now im not saying it'll fit, I really dont know, it looks like it will. But i just built a custom enclosure for a JL Audio 15w6 to fit under the drivers side rear passenger. My enclosure still retains the back portion of the seat, and the bottom portion of the seat is the box with a custom upholstered cushion to match the factory seat. I didnt sacrifice any of my rear foot area, but I really dont plan on having any passengers unless some OOmpa Loompas want to ride along considering there is no space for full size adults back there anyway. You just have to be willing to fork it out if you want a crazy ass sub to fit and still sound and look good at the same time. I do have pics of this box as it was being built. I will post final pics when it comes back from the upholstery shop.