White gas is the best fuel for availability and performance at altitude. If you have cold issues, think thermal clothing, layering. If you have have insulation issues, solve them, make yourcamper efficient. Use a heater to burn off condensation but not actually keep the camper warm. And you will need to ventilate the camper to reduce moisture build up.
For heat sleeping, consider an electric blanket. The few people I have met with them seem incredibly happy.
But white gas stoves and heaters put out more BTUs than any other choice at high altitudes. Hence it is the choice of mountaineers.
For average guys in North America not doing anything extreme, propane is a real simple excellent choice.
This is my go to choice, Dad bought it in the 1940s and it still works like new at any elevation.
My only recommendation, only burn white gas. Gasoline for your RV contains all kinds of additives which can create problems. I remember in the 1960s Dad used gas for a bit..... it would not light easily and it took longer to boil water. We switched back to brand name Coleman White Gas and 50 years later it still runs like new.
We have used it a few times over 9000 feet and not noticed any decrease in performance. And they are simple to refuel.