I recently bought a cabin that is off-grid and at 7500' elevation. I have camped at high-elevations with a Mr. Heater that has an O2 sensor with no problems, but just heard that they don't operate well above 7000'.
My impression is that the problem is more frequent shut-off than at lower altitudes. Do you have experience with vent-free propane heaters at high altitudes? I don't want to subvert the low-oxygen sensor altogether.