I think I'd try opening some vents and windows to get some air flow to possibly reduce the humidity instead of cutting a hole in the floor. How about running the A/C?
If you don't have them the Maxxair covers over the vents are a good investment. It allows the vents to be open in all kinds of weather. They have a new one that is able to be tipped up for cleaning and has more openings for air flow.
Just my $.03 adjusted for inflation.
We are in the Chicago area having much the same humidity condition and there is no build-up of moisture in the RV