****UPDATE:
Cliffs: No good. Don't waste your time attempting this.
Long version: So I finally did some work on this over the weekend. I started by taking the lower rear seat and the passenger seat out, and pulling the carpet up. I found a ton of what looked like birdseed?? under the corners of the rear seat cushion, along with some crusty stuff that looked like dried up dirt / mud
, a small fortune in old, dirty change that had fallen down and gotten stuck under the passenger seat over the years, and a little pin for some really obscure band I've never heard of. I was sort of hoping I'd find some better loot
Anyways...I didn't want to drill through the floorpan for any reason, so I made a pair of crude brackets out of 22 gauge sheet steel that would allow me to bolt the amp down securely, yet not have to drill through the floor. These brackets were held with lag screws to the bar running underneath the seat. 4mm studs were placed in the appropriate locations for them to extend up through the carpet and the mounting points on the amplifier, which was held to the studs with hex nuts. Holes were also drilled in the brackets for the rear seat bolts to pass through. They were ugly, but functional, and they held the amp really well, so I was happy with them.
The amp fit perfectly between the seat rails, sat very securely and solidly on the brackets, and looked like it was going to work. That is, until I put the seat back in. The bottom of the seat scraped along the top plate of the amp, and also dragged on the sides of the heatsink - and that was without anyone in it. With someone sitting in the seat - forget it.
This space may be suitable for mounting some sort of very thin component (like an active equalizer, or component speaker x-overs maybe) but will not work for an amp. The one I test fit was 2 1/8" thick, and didn't even come close to having the required amount of clearance - I very much doubt that an amp is produced that will be thin enough to go here. Too bad, it would have been perfect.
Now, I have to figure out where to put this thing in my trunk.
Really didn't want to put it there, but I don't really have much choice I guess. Anyways, just wanted to update in case anyone was interested.
**EDIT: And yes, the ABS computer and associated wiring is the only component under there (at least in mine). It's a rather large, thick box that is held with 2 10 mm screws to the bar running under the seat and the raised bump that the right rear seat bolt goes into, mounted on the far right side. There was also a mysterious threaded nut welded to the floorpan near the center console area that went straight through to the outside. This was obviously factory installed, but I have no idea what it is for - in my car, there was nothing occupying it.