IIRC, the tacomas are VERY hard to fit subs under. Clarion makes a really low profile sub that should fit under there with a custom made box.

I've got these for sale if you are interested : 10" MTX 8000 Sub and Orion Cobalt Amp For sale That should leave you enough money to get a custom box built if the thin box that I have wont fit... (PS, sorry admins if I am breaking any rules)