Have you tried the Mr. Buddy propane heater. I know that they are supposed to get more moisture in the air but people I have talked to who use them swear by them. They are relatively cheap, easy to move around where you need the heat, have the ability to mount to a bulkhead, and have an oxygen sensor to auto shut off, (although you don't want to count on it). I have limited space to have a built in heater. The main cabin is pretty much off limits as I don't want to give up seating area so it would mean installing in the cuddy. I know that others have done so, including Renn. I don't do much extended fall camping so I am usually trying to take the chill off while fishing. I use one of those Coleman propace catalytic heaters, (the one with the round heating surface) and it works pretty well. I usually have a couple of windows cracked so moisture hasn't been a problem. It will last all day with a 1 lb bottle. Just a thought.