Electric heater vs using furnace in fall?

I have used a propane stove to heat up both my camping van, and my 18 foot TT. I have a CO detector in both, with a read out of CO available. My Wave 3 in the van would bring the CO up to .40 within 30 minutes. I don't trust it at all, even though it has great reviews here. I never got the CO to register at all in the van with the Coleman stove on high, and shut the thing off due to the heat, rather than any sign of CO. In the TT, I have run a burner on high under a tea kettle, or a big pot of water, and found it heated up the trailer quickly and easily, with no CO reading on the detector. I would not run the stove while I slept, but feel comfortable heating up a two gallon pot of water, and letting the pot sit, with a lid on, over night to keep things from getting cold. I am currently looking for a direct vent propane heater of some sort, having an old and cranky furnace that drains the batteries too soon.