I think Kevin missed that you are talking about a "Cameo" truck with the fiberglass bed side panels.
Yep.
If it did crack the underlying fiberglass mat, what I'd do is scuff the back of the panel, apply some resin and embed a piece of fiberglass cloth to reinforce it. Then you're going to have to sand, fill and repaint the outside. Not a fun job, it'll be messy. If the panel is removable, do that so you can lay it flat so you don't have resin dripping on you. I crunched a fiberglass cab step on my '99 Ford, and managed to repair it. Had to farm out the painting and re-application of the bedliner tread material, so it wasn't cheap.
