Options for in cabin heaters
Since you''re way up there in Cold Country (as viewed by those of us down in St. Pete!), you get to pick 2 out of 3: inexpensive, useable at the dock, and/or safe in a confined space. Regretably, we don''t get all 3.
Fuel heaters can be vented externally (e.g. propane & diesel/kero fuels) in which case they produce dry heat and the CO is sent thru a deck pipe. They require permanent installation and a few hundred dollars. Non-vented fuel heaters (catalytic heaters, kerosene space heaters) are warm, cheap & portable - but all the CO is vented into the boat''s cabin. Electric heat would be tough to support, even with a sizeable inverter and house bank: e.g. one 10 amp 110V AC space heater (typical) + inverter ineffencies for a 10 hr period = 1000+ amp/hrs. Cheaper to buy a 10 mile long yellow cord. <g>
You sound like a good candidate for an inexpensive kerosene space heater. Check stores that sell wood burning stoves or have a good hardware selection. Leave a hatch cracked for good ventilation and don''t leave it lighted should you spend the night or feel like taking a nice long nap - it might be too long.