We painted some fiberglass bumpers. We did a lot of prep work on them to make them flat as steel (almost Lol!). Painted them PXR Brilliant Black Pearl Coat (Chrysler color) and they looked amazing. A few months later they look like fiberglass. The paint shrunk a lot and has a slight waviness to it. Hard to describe. I might be able to wet sand them but I shouldn't have to! We have painted plently of fiberglass with Sikkens and it looks just like steel many years later.