So I have had some water ingress around one chain plate and the deck between the chainplate holes (the U-bolt type chain-plates) has gone soggy. Picture below.

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Any pointers on how to repair this please? I will dig out the rotten deck from below and then should I fill this with epoxy/matt? Fibreglass board (e.g. G10)?

Another thought I had was to preserve as much of the lower fibreglass layer as possible, should I drill a series of small holes and use them as access points to dig out the rotten deck?

Pointers please!

Trev