Not for the XFL, but this is what we did for a small single 12" sealed setup for the same car. There is more then enough room to build something similar just larger and go ported and still have a decent amount of room.
*note, the wiring is not ours nor did we run it. I was just requested for the enclosure and then it was picked up and installed. Sounded great when he came back by..but not my favorite choice in product used in this application. It did work rather well though, I was actually impressed by the performance.