To clear up some misstatements here, the Buddy heater has a Low-oxygen sensor. Low Oxgen can be caused by several things and CO is only one of them. Buddy Heaters do not have a CO detector so adding one into your camper is a great idea.
As far as having something for supplemental heat, the buddy will work just fine at cold or altitude if you use a 20lb tank. I run mine from an 11lb and 20lb tanks in the winter while ice fishing and they do great. Below zero and they start to ice up if your'e running on high, but they pump out enough heat its not needed.
My biggest recommendation is to have sleeping gear and clothing rated to the weather you will be in. Have a plan if the heat does fail. I use heat to keep the tent or camper warm when we cook or get dressed. The heat goes off or on low while sleeping. Let your insulation keep you warm.
I have done the tent camping no heat other than cook stove. At my age I am treating myself to more to comfort for now.