My boat is in Florida where it rarely freezes, and usually gets up to 50 during the day even in mid-winter. Still, living aboard can be chilly. I use the oil-filled electric radiators and they work well without dangerous hot spots. They are bulky and you have to find a good spot for them. I can plug one in port and another starboard and run them up to 3000 watts total if I shut off the electric water heater. Perhaps you could run a couple (1500 watts on full) from your second ac shorepower.
I use an electric blanket running through an isolation transformer. Very comfy.
I lived aboard in New England one winter and used a small coal stove. It is far easier to use than wood, and coal (anthracite, not bituminous) is cheap and clean. Does not turn on and off though - you must keep the fire going.
I don't know if you have insulated your boat. I did mine with Reflectix (a lot of posts about it) and it was easy (all the work is in removing panels) and works well. Much more comfortable now.
1975 32' Flybridge Sedan, twin Perkins 6-354 diesels, 1:1.53 velvetdrives, 16 X 19 props. Merritt Island, Florida
