Here we go......
We went through this last winter and when I told what I do I got jumped on from all sides, but just for you:I use a Kerosene, unvented heater and leave the drop boards out of the companionway as well as the cabintop hatch open. This causes a draft like the indian tee-pee's and there is no smell or chance for affixiation. The heater costs about $200.00 new and uses a gallon of kerosene in about twenty-four hours. It puts out 8,000 btu's. I have never slept with it on and don't ever plan to. The idea of an untended open flame on a boat scares me to death and I don't care if it's vented or not. I also don't sail in subzero weather so it's not a problem.Just crawl in the ole' sleeping bag. And, that's the all of it... Good Luck and for all those people ready to jump down my throat, I do know what carbon Monoxide is and my Monoxide alarm tells me there is none in my boat... See Ya