I've just started stripping out my old interior and I found this fiberglass window mold.

Which came off the kitchen panel opposite the sliding door,
It's also revealed some rust in the panel. Not much but that's what I need advice about really.


here's the worst bit.

Like I say, not really that bad but I'd like to get it sorted whilst everything's out.
Should I cut it out and investigate below? There's a bit of a rash on the outer skin?
Secondly, I'm assuming that the fiberglass window surround was made by the conversion company, is there a steel factory panel
version that was used on caravelles etc? My rear window has it's own steel surround.
Thanks for any advice.

J