Why didn't you ask at the "home" forum for this? Me and Nam would've got you going, but I've done some of the work. You can fit 3x8's ported if you wish, but your enclosure skills had better be decent. You could fit 3x10 sealed with the same enclosure restraints (the window thingy in the middle where it humps out kills a really nice, straight enclosure). 2x 12 can fit, but depth really becomes a problem. Idon't think anything over 4" deep is going in there.
Now, you can do some really neat stuff under the rear seat (as long as you never want o fold it down again). 4x8 sealed looks pretty simple with fiberglass. Hell, I can fit my Power 1000 under there twice, so there's quite a bit of space.
You have options, the toughest part of working on that vehicle is running the wiring. That tiny little cavity behind the head unit is NOT made for man hands.
BTW, I think you'd be happy with a pair of 8's tuned 32-35hz. You can always add another later. Or, you can try a single one poked into the factory box. The Sundown e8 needs a 1" spacer ring, and it will still fit behind the factory panel. I'm TRYING to port the factory enclosure, but I just can't work the numbers out //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif I can run tubes out the side, but I'd have to leave the back panel off- which is an option. I could make a pretty nice replacement to make everything seamless. Hmmm