... but do you really want to encapsulate and trap the water? That would lead to bigger problems later.

You need to grind out the skin and remove the wet stuff, then epoxy in new blocks of coring and re-glass. If the core is wood you need to remove and replace. You only need to remove one side of the FRP skin (inside or out).

If foam cored, I have heard of people using vacuum bagging and sustained vacuum along with many small holes to remove a high percentage of the water over a period of several days or weeks, following up by sucking-in epoxy with a vacuum. I haven't tried that.

If you can get hold of a moisture meter it will help. I bought one -- it's good to have in one's tool arsenal if you're boat shopping or dealing with issues like you encountered. They're expensive, but it pays for itself if it keeps you from hiring just one surveyor on just one boat.