Moisture is like "a soft spot" same as in a car or a house or an RV.
The only way to fix it is to open it up, and to keep removing stuff until you get to sound material......
My experience with boats, houses, old cars and RV's is that it's ALWAYS worse than you thought.
So, unless you are Mr Toolguy and know how to do it (which you are probably not, or you wouldn't be here asking the question) or if you have a LARGE check book, you are not going to like the rest of the story.
Currently boatless but looking. Avatar is my first boat....Holland, 1965 ish.....