Did you take any pictures of the gel coat cracks? Not trying to slam NL, just wondering what the problems were.
The biggest problem with bead board, AKA Expanded Polystyrene Foam (EPS), is that it is a weak core material. Extruded Polystyrene Foam (XPS) is preferable but more expensive and harder to get. It absorbs less water but also has higher sheer and bond strength. My 1988 and 1998 Big Foot both had XPS, but the 2008 has EPS I am sorry to say. If you had the ability to influence them, I would request that XPS foam be used even at a price premium.