On airplanes when there is a crack in plexiglass the procedure to stop the crack from creeping is to stop drill. Stop drilling is drilling a small hole, the width of the crack, at each end of the crack. If it were me, I would stop drill then apply the Captains formula.
Here is something else:
Polyester resin will stick to epoxy resin and polyester resin however epoxy resin will only stick to epoxy.
What this means is if your fiberglass used epoxy, you can patch with either however if they used polyester then you must use polyester.
I wonder about Grollia glue in the wet area as it relies on moysture to cure. It might work however you would have to sand the excess down as it expands when it cures.
Merry Christmas to all.