My boat is cold molded with epoxy. I had a fiberglass skin everywhere underwater except the rudders. During my last haulout I found worms in the rudders. I don't know how they got past the epoxy or how fiberglass could keep them out, but the rudders are now skinned as well.
Ship worms can get the wood if only resin covered. A fiberglass or copper skin will keep them at bay. They do not like ceder, teak, ironwood , swamp cypress and a well painted bottom. Get a nick and there on it. They just love white oak dead wood areas.