We do a lot of winter sailing, liveaboard life in the PNW. Have found that running 2 110 volt heaters can overrun the dock power. Trips the breaker. Still, running 2 heaters on Med. is better than one on high.
We also have an Espar forced Air Diesel heater, the combo gets us thru snow on the deck weather.
Boat was in charter out of Bellingham, WA for ten years, no problems with cold.