the boat stays in the water. Here in the PNW the water never gets that cold. The water will keep the boat above freezing temperatures.

On my boat the hot water heater is close enough to the engine that leaving it on warms the engine block - the reverse of engine heated hot water. The hoses from the block to the water heater are only a couple of feet long. Even that is not necessary. I also keep a ceramic heater on in the boat so it is comfortable when we visit.

We intend to spend the next two nights aboard.