That was my plan. I will epoxy first. Tech sheet does not list paint as an approved substrate. Though, I guess fiberglass is technically "epoxy". I didn't want to weld that area and twist the window frame. VPA filler has been recommended here a few times for use as a filler between quarters/roof.
DESCRIPTION: Polyester body filler primarily used as a filler on SMC and fiberglass panels. Can also be used as a light duty-bonding adhesive for non-structural repairs such as backing repair strips and old style fiberglass panels. This non-shrink polyester body filler helps prevent repair mapping on seam lines over fiberglass
APPROVED SUBSTRATES:
Steel
Aluminum
SMC
Galvanized Steel
Fiberglass
Most Rigid Plastics