I think I'd actually go for the L5 because of cost and power handling.
It shows a mounting depth of 6-13/16" which should be doable, I want the carpet on the side door to be flush with the front edge of the subwoofer surround. May take some creativity with the fuse box location and some other things but I think I can do it with the help of a fiberglass guy I know.
As for sealed vs. ported - for a given sub a sealed box requires less volume than ported so that would be the way to go. They are also more forgiving when run on the small side.
I have a 15" L7 in my GTO right now, recessed into the tire well, and the box is undersized by a couple of cubic feet. It still sounds really good, and LOUD (of course 1600 watts helps too)
If all else fails, the 10" wouldn't be a bad choice I'm sure. I'm not looking for anything obnoxious like in the GTO but always like to run on the extreme side of things
Sorry for the offtopic posts