So Monday I am going to have my local stereo place put in the amp and a sub box (pair of 10" subs) when they do the door speakers.
When I went to there today, I asked how much extra it would be to upgrade to dual 12" subs, and it was only an extra $40, so I went for it.
So I got 4 Alpine SPS610 speakers (one for each door), a pair of Alpine SWA12 12" subs in a ported box, and an Alpine MRV-M500 to run it all.
I had them take out the factory sub box, and put the new amp in its place (you can see the light through the factory sub grille).
Now my wallet is $1000 lighter, but I know the the install is done properly, and if something goes wrong, I know who to call.