There is a 4" high by 12" long by 1" thick backer board behind where the hooks are installed. I was just at the factory and asked this same question because I added a hook on my old PC. I did not hit anything with that hook. Bobby and I went looking at how the rear end cap is make and mounted. I want to put a hook in the new PC but have not figured out how just yet.
I'm not anywhere near my PC right now, but I was wondering if you could simply cut a 4"X1" board to the desired length, bevel the ends for appearances, and simply glue it with some sort of really strong epoxy or mastic glue to the inside of the rear cabinet, paint it white to match, and then just screw your hooks into that and on into the fiberglas beyond. Unless you plan to hang something very heavy, that ought to do the trick and it is out of sight inside the compartment. Just a thought.Jerry