Honestly dude, I have mine mounted to the box and they are fine. I figured out the problem on my amp too, for some reason I had to ground the outer connector of the output going from the sound processor to the amp. It was back feeding the signal into it and shutting the DC audio amp I am running. All is good now.
My next thing to do on mine is to get some 1/2" plywood and make it the same size as the top of my box and put my vibration isolators between the box and that sheet of plywood and mount the amps to the plywood itself. Just for added protection as all. Here is where I got my isolators from:
http://www.grainger.com/category/cylindrical-vibration-isolators/mounts-and-vibration-control/material-handling/ecatalog/N-9tu
they are a little pricey but I will admit, they ship really fast and are a nice quality. I am running the ones that are for 125 pound downward force and i think it's 25 pounds of sideways shear limit.
I think you can fit the amps underneath the covers on the rear hatch area. Only problem with it there is that you can't get to them when you need to adjust something or replace a fuse if one were to blow for some reason. If you want something cool to do and depending what the bracing looks like behind those plastic panels, you can try to route out part of the plastic panel and mount the amp to that and have it so the amp is visible. Like mount it so it is at the area above the little wheel well bump and toward the liftgate as much as possible. I think that would look pretty nice even though you don't have that much of a viewing area on the sides.