A couple of problems that may present themselves later. When it's time to remove, how much work is it going to be to get that stuff off? If it's not formulated for fiberglass, it's possible it's going to start peeling along with turning yellow because of UVs, there again... in the future.
I know no personal experience with the product and truly do hope it works for you and meets your expectations.
Let us know how it goes!!