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