Properly sealed, they should stay dry. If they're epoxy bonded into a single piece, they, like a glulam, should be as strong as steel and stronger than solid wood beams. I've bonded many keels, ribs, bulkheads, etc., with epoxy and never had a moisture issue. In theory there is a micro porosity in resin, but items I've cut open, laminated wood, even plywood, bonded and sealed in epoxy, never have shown any sign of moisture or recorded a higher moisture content that kiln dried wood.
Although in some fiberglass boats, Bayliner especially, I have found shoddy workmanship in interior fiberglass work even though the hull was well done. It looked like 2 different crews worked on different aspects of the boats. One professional and one amateurish.