Did the surveyor discuss the fix for the deck problem? If he's certain that you will not be able to get insurance because of the moisture, did he provide you with the moisture level? And is the plywood core delaminated from the deck? I would start with the surveyor and get a full description of the problem, which you probably have, and a full description of how he would go about fixing it. This will give you an idea of what to do and possibly a list of specific questions for this forum and a nearby boatyard.
Good luck! I hope that some of our knowledgeable members post additional responses.