I bought a heater buddy and love it. It has O2 depletion sensor and I have a CO monitor on the boat. I have not slept with it on, but it has helped with my winter projects. I've run it for two hours and the CO alarm never went off. I should note that I have a cabin solar ventilator and louvered cabin door. I would not mind sleeping with it on though, this is no different that an unvvented gas stove in a house as far as the CO goes. My dad has a fixed propane system on his boat with 10lb cylinder. It is in an overboard draining locker and sealed from the cabin. Propane on boats is not uncommon. Look at all these camping stoves and heaters for use in RV's and Tents, you must use good judgement. That said I have two little kids and the likelihood of sleeping with a heater on in the boat with them is about nil. jh