Yes that box is with the stock spare, I just sketched it out real fast, but it would be to exact measuments to fit in between the stock spare on the left and the right fender well.
Yes thats a big port //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif, to get those Tang Bang's pounding you want to have them in a ported box. I bet these two 8's will be 3 times as loud as your old 10" sub and they will hit the lows like crazy. I'm not sure what the exact port area is, but I'm guessing it's gonna be similar to that shown above.
I'd say it's about 28" WIDE x 25" DEEP x 9.5" TALL That would cover the entire bottom and give you room to mount your amp on either the right side of the box where the right fender well is or if your amp is only 9.5" tall you caould mount it on the back of the box where the rear seats are. Remember this box the subs and port are facing the rear hatch with about 4" of spacing between the box and the hatch.