Fixing cabin wall plywood rot (Leaky portlights behind FRP)

[DocHolliday]

There are epoxy saturation products specifically made to soak into, strengthen and reinforce rotten/punky dry wood in houses. I'd dry the mess out totally and use that, and then rebuild lost wood with epoxy and glass. The final result might even be better than when it was new construction.

[WaldPinkler]

I've come to the conclusion that ply wall isn't structural. I mean I can put a scraper in between the fibreglass wall and the FRP the whole way round on one window. I think it's just a convenient/fast way to finish the cabin wall, thicken and insulate.

It's open at the bottom, I'll remove any real rotted parts then fill.