What most people don't realize is when you buy a 'new' RV, it's not really new. New to you but keep in mid that from it's 'birth' it sat outside, at the builders lot and then hauled down the road by a transporter to the dealer and then on the dealers lot.. Out in the weather, in the snow and rain so, if it's leaking now, it has been leaking since it's 'birth'. Consequently, you probably have ongoing water damage already.
Water leaking in causes mold and rot whether you can see it or not, it's there, between the outer skin and the wallboard.
Myself, I prefer as little as possible roof intrusions. Every vent and ac mount is a point of water entrance but it sounds to me like you have a sealant issue. Either the builders forgot to seal it properly or one of the 'Amish' craftsmen didn't bother to apply sealant. Nothing new there.
I'd be way more concerned with the water intrusion issues that an ac issue. The water will kill your RV and it won't take long. What you wind up with is a project unit that's not worth anything except to you.
