Looks like from reading other posts (should have done that first I guess) that a dehumidifier or insulating is the only solution(s).
In a nut shell, you need to get the indoor dew point (humidity--the temperature when dew starts) above the coolest outside wall temp. There are several ways:
* Insulate to increase the wall temp, but be careful; if the air circulates behind the insulation, water will will condense and you will have mold. Insulating a boat is a tricky business.
* Limit humidity generating activities. Cook with tight lids. Shower ashore.
* Dry the air with a dehumidifier. Search the threads; I have seen some very small ones listed.
* Skip the Damp-rid buckets. Each can absorb a few pounds of moisture, and you can exhale that in a night. They are ONLY for sealed boats (no vents). Waste of money in this case.
* Heat, but with a window (better, some other vent) cracked a bit. The cracked window needs to be in a heated space.
The air out side the boat is certainly drier in absolute humidity (pounds water per cubic feet) than inside. It is a misconception that a heater can "dry" the air; raising the temperature of air lowers the relative humidity. However, since the wall temperature is still warmer than outside, it helps. It is people that put the damp in the boat, not the outside air.
* Run a fan on low. Air movement increases the temperature near the wall and thus reduces condensation.
* If windows drip, storm windows will fix that. Exterior covers help too.
Sail Delmarva: A Few More PDQ Upgrades
Sail Delmarva: Salon Window Covers
* Heat the whole boat, not just what you use; the cold rooms are going to see the same humidity as the heated rooms, but cold air can't hold the water.
Like a house, it's a little of everything. I've taken steps and don't get condensation, even in freezing rain. Nice dry air in the cabin. When I bought the boat, there were some drips, one being a hatch right over the pillows; one drop of ice water every 10 minutes.