You are "In Tune" and sounds like you are doing great. That moss is excellent as it will dry and retake moisture. I had a humid hid filled with that when I first got my fella and he rarely came out. It had a lid on it and the whole works. I eventually took the moss out and scattered it about the cage.
DAMP VS Wet is a separate matter. If he is in damp moss he's just fine. My favorite authority on boas, Gus Rentfro will tell you soaking in water for hours is NOT good and is usually a sign of something being wrong. Also prolonged periods in water can lead to what you are worried about. That said, moss that is damp should be just fine.
There are very good articles and posts regarding care. I can't begging to link them all here, but I personally like the humidity HIGH 70-80% as long as there is no standing condensation. I find my snake rarely drinks and uses both warm and cool side of the cage equally.
There are various opinions and there is no 100% set in stone way to do things.
I have a few long posts in this forum about caging and can help you with that if need be.
Keep him enjoying the moss.