I agree with the use of Fa-stone, but I think I'd coat the damaged area first with some epoxy resin to seal it up against any water intrusion into the polyester laminate. I would then apply the Fasco epoxy filler while the epoxy resin is still tacky to insure a good bond.

They make nice product.
Sand it early to avoid rocks.

Thanks!
 

Thanks for all the advice y'all. I will try the Fasco. I think the epoxy idea first would be a great recommendation. I'll report back soon I hope.