Hi
I think we are dancing around theories of chemistry or issue.
Polyester resin dissolved in styrene is obliviously going to work to a certain extent on GRP (Styrene) and is also going to bind fairly well to wood ... for a while but wood's makeup over time will change resins, sap, shrinkage etc combined with impact strength may lead to joint failing. Having said that the joint will allways fail if the chemical or mechanical bond is broken ... so which is right really ...?
Silicon bath sealer works well on bath edges ... until the bath rim either sinks or the bond is broken mechanically ... or chemically in deteriation
Epoxy is also a good glue bit is not chemically matched to GRP ( Styrene) so we should assume only mechanically bonding from the outset?
If there was a perfect solution i'm sure we would have stopped discussing some time ago....
Just my thoughts,
Kim