A few years ago I removed and rebuilt the SS arch FRP sound box. The PO had used the box as a snap mount for the cockpit enclosure and as a result water leaked in and destroyed the speakers and volume control.

Brought the box home, removed all the old snaps, speakers (turned to dust) and volume control (frozen). Found replacements online that fit the original openings and speaker register. The box cleaned up nice. Used an epoxy filler to fill in all the cracks and holes, sanded and finished with an exterior industrial grade plastic acrylic spray paint. Really pleased with the finished repair work. That was five years ago and it still looks like new.