so both front and rear should still have antifreeze. I did flush out the garage shower - its in the garage but probably gets plenty cold. Since the boat is in the water, I'm not too concerned about the engine, it is full of antifreeze so the heat exchanger might be at risk but that is a substantial thermal mass low in the boat full of salt water. The water maker wasn't flushed, so still has antifreeze. The domestic fixtures seem like they would be most at risk. Also maybe the domestic hot water heat exchanger though it is below the waterline and close to the hull.

I may be able to contact someone there and get a heater in on Monday. The advice I got from people on the dock there was it rarely gets cold enough to worry about, and the water temp doesn't get real low until February which tends to keep the boat a bit warmer.