We like to work on the boat during the winter. The full cover makes it tolerable to do short amounts of deck work. The sun warms up the air inside the cover but the cabin always starts out much colder. When the bilge or engine covers are pulled off, the temperature just plummets along with my desire to work on the engine. We were using an electric and Mr Heater portable buddy heater. Unfortunately our Buddy heater died. Two replacements of the same model have been ordered and both gave off some heavy fumes, made us both very tired (yes, big sign of CO poisoning and low oxygen) even with the hatch opened a bit. The electric heaters are helpful but don't do much to keep the cabin warm on its own. The yard has GFCI outlets but I'm not sure how many circuits are by us. What do you use to stay warm in the winter?