Musty or Mildewy!
I agree with taking matresses/cushions home, but what about the rest of the boat? In the Seattle area, we leave the boat in the water year round and don't winterize. But, we do have plenty of moisture and humidity which contributes to mildewyness (I like that word). My solution for the last 10 years or so is to leave electric space heaters on 24/7. I keep the temperature at a constant 50 to 60 degrees (just to be able to visit a warm and cozy boat on my ocassional visits). A temperature of 35 to 40 degrees would be just as good. The constant temperature and air flow virtually illiminate any condensation and resulting mustyness or mildewyness. It's a little expensive, but the results are worth it.