I've never seen fiberglass dent. Those Cameo bed side panels are hard to find and like any other fiberglass can be tough to repair. If it has a depression where they toy hit, it may mean there is structural failure of the fiberglass. It's been decades since I did any fiberglass work, so not sure how to suggest further inspection/evaluation to see what the damage is, other than to remove the panel entirely. Lots of work involved and makes me cringe, just thinking about it.
I think Kevin missed that you are talking about a "Cameo" truck with the fiberglass bed side panels. I tweaked your thread title to add that detail.
