Thanks for the suggestions! All of the boat's shore power system is brand new, she previously only had DC power. I agree that the electric heaters scare me too. However, it looks like you still have to plug the oil heater in. Sorry if this sounds silly, but how are the two different in that department? What makes the oil heater safer if it is still part electric? (Originally from AZ, don't need many heaters there!) I do have some of the small propane heaters also.
Admittedly, my evidence is mostly anecdotal, but I've heard of many fires caused by heaters with exposed elements (the forced air type) where the air intake clogged with garbage, or they fell onto something and the tip-over shutoff failed, or the overtemp shutoff failed and caused fires.
I've never heard of this happening with an oil-filled unit. The element is submerged in oil. It remains submerged and contained, even if the unit tips over. The total power of the unit is dedicated to making heat. Some power of a forced-air unit is directed at driving the fan.
Any heat producing equipment that is left unattended, is dangerous. I just feel that the oil-filled units mitigate the danger a little bit.
Also, I'd like to apologize- You should NOT adapt the Coleman propane heater to a larger sized propane bottle. My earlier information was incorrect.
Some people feel that the disposable 1lb. propane bottles are dangerous because the little Schrader valves are cheap and can leak after unscrewing the bottle from the appliance.
This is true, but you can mitigate that danger by leaving the bottle screwed on, until all of the fuel is consumed. They rarely leak once attached to their appliance.
I have also just found (on the web), 1lb. propane bottle caps that allow them to be re-filled. I cannot recommend these, as I don't know anything about them. I am considering buying a pair and trying them out, and I can report back once I've learned something about them.