we had Guenevere on a lake for a winter and I was worried about freezing. It was in Georgia, so it was not to bad and the dock I was on had electric power.

What I did was purchase a very low cost electrical thermostat at a hardware store, and an old trouble light. You know the type of trouble light that has a bulb in a small cage on what looks like an extension cord. I then wired in the cheep thermostat and put an industrial lamp in the trouble light. It would only come on when the temp in my boat when the inside temp went below about 40 Deg. F. Worked for a couple of winters. Just an idea....

Greg