I have a 1968 GS California that has some rust out around the rear windshield-darned vinyl top. It's not in the channel but the vertical metal on both sides of the glass. My question is whether fiberglass patch panels would be acceptable for repair. I plan to POR-15 everything before covering it again with the vinyl top. BTW, this car will only be a cruiser, not a dragstrip terror.
Proper way to fix that area(s) is to fabricate patch panels from a scrap trunk lid. Cut out the old area so you have good, clean, solid metal. Weld-in the new patches and grind the welds smooth. You need to use SEM weld-thru primer for best results. Fiberglass won't last because you need to stop the corrosion and repair with metal.