If you are on lake Lanier, your issues are likely the ambient temperature/humidity swings, as noted by
@TimFromLI. You can heat the boat up to about 75 degrees (maintain all surfaces well above highest seasonal ambient dew point), or seal it up tight and run a dehumidifier with about 50 pint per day capacity. You will need to connect a drain hose to the unit to drain the condensate outside of the boat. In your area, the unit reservoir would need to be emptied multiple times per day until you get the boat dry, and possibly for the entire season (depending on infiltration) - making the reservoir impractical. Mechanical dehumidification will only work if you can seal the boat to largely prevent ambient air from getting in. You may have to run a heater in addition, but I would try the dehumidifier alone first. Due to inefficiencies, these units put off a small net heating capacity.
If your boat is in the water, the inner hull surfaces may be essentially at the water temperature. So, you will need to reduce the cabin air dew point to be below the water temperature to prevent condensation on the hull (assuming no core). This will give you some idea for dehumidifier specs. Get one that can maintain a dew point at or below the water temperature.
As
@jssailem states above, the liquid water in the boat will negate efforts to prevent condensation as this water is continuously evaporating into the bilge air, keeping it saturated. This will work it's way into the cabin.
If you were in a more northern climate, or west in a drier climate, heat and ventilation would take care of it. Where you are, mechanical dehumidification, and making the cabin as air tight as you can, will likely be the only way to take care of it. Obviously, you should shut down your propane system, remove flammable liquids, take measures to prevent flammable vapor build-up, prior to sealing up the boat. It doesn't have to be totally airtight, but any cracks wider than about 1/16" should be corrected. Open vents, louvered openings, etc. could render the dehumidifier ineffective.
Good luck.