Can pretty much use 303 on anything including the fiberglass if you want to. We just use it on seals (slide, doors, hatches Etc) though. Got other preferences for the fiberglass. 303 is great stuff. We've been full timers twice and it holds up well. Been using it for well over 10 years now.
John and Rebecca Dickson
Emma-8 / Little John-5 / Iva-1+
2013 Ford F-350 Lariat FX4, CC LB PSD, DRW
2015 Jayco Jay Flight 28BHBE (#8)