Turns out the water dripping down our walls was not the work of a malevolent marine imp, but rather a little process called condensation. Now, condensation is something that we live with on a regular basis. It's the sweat on the outside of our soda cans, the dew on the clover field, the water dripping down the walls of our bathroom. If you can't tell, I'm really not enjoying that last one.
I had, also, never considered how condensation works, but thanks to my awesome live-in science guru I now know the entire process. In the winter when the inside of the boat is warm, the air can hold more moisture, but as that air travels to the sides of the boat where it is cooler it loses energy in the form of heat causing the molecules in the air to become closer together and move more slowly. H2O molecules in the air cool down as well and condense into water via a phase change releasing energy as heat to the cold surface (about 585 cal/g at 20 deg. C - Vlad made me write this part, I swear). The process reverses in the summer (i.e. the water condenses on the outside of the boat where the warm outside air hits the cooler air against the boat.) Hence the reason why the air feels more humid in the summer, but the inside of your boat is like an Amazonian rainforest in the winter.
Solution: A dehumidifier. Sixty dollars from Home Depot.