I just mounted mine to the side of the subwoofer enclosure. I know this isn't the "professional" way to do it, but wuth quick-disconnects I can take the unit out quickly for more storage space when I need it. If I was going to install it permanently, I would have installed it under one of the seats, probably the passenger's.
I forgot to mention that I wanted to keep the usuability of my cargo area. I ended up putting it under the drivers seat. I also put my subs in two seperate boxes, one on each side in the recess area in the very back of the hatch so that I can still put my seats down and haul stuff without taking them out. I will post some pics as soon as I get the boxes carpeted and everything. 2 12"s sounds awesome as hell in a hatch though! (This is my first hatch and I had always heard that acoustics were better in a hatchback.)
my hatch was not compromised too much for useability. i mounted the subs in the spare tire well. you could put whatever you wanted right on top of the subs' carpeted grilles (made from wood and metal). the only compromise was that the spare tire had to be relocated onto the floor. the rear seat could still fold down completely with the amp rack still functional. by the way, one sub grille is removed for the photo:
I mounted my amp to the bottom of the drivers seat pan so that it moves with the seat. It was pretty easy; once you hve removed the seat you can easily move the wireing and attatch your amp directly to the pan.
My amp is upside down screwed to the seat pan; it is not attatched or supported by the floor. My connections come through a hole I cut in the carpet at the mid point of the seats travel and when wrapped with cable housing appear to be stock.
I would be concerned about the airbag wiring harness, which has had problems if the amp is in that location. Although that would be safer for the amp, and might be harder to swipe, having an amp in that location might have a few size issues.