in my old 95' xlt, I installed a simple to make (but painstakingly long time to make) false floor that went up to the box, I covered it in gray carpet that matched the interior, off of ebay. then put the amp in that. i completed several different installs in that vehicle, and the amp had to move several times. a good one (unless you have an ungodly amount of bass like me now) is attach it to the box, behind the box between the rear seats and the box. other than that you are kinda screwed. under the rear seats was never possible for me because I had my gps stuff under that, but you may be able to put it there.
