I basically did the same thing JCG mentioned above. I cut out several MDF boards to put on the back side of the carpet to anchor the amps to. I did however drill two screws into sheet metal to hold the MDF in place so the amps would not wobble. They are above the splash guard so I am not worried about rust or anything.
I have a new sub box, a pair dual 10" Power Akoustics inplace of the one 12" sub in the pictures below. But you can see how clean the install came out.
Before being mounted to the MDF board behind the carpet.
After placement was made and set.
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