Propane boils at -42C. There is no need for complex heaters or concern. I used it to heat my home for over 25 years in a climate similar to where they are going. Depending on the size of the tank, temperatures would have to be sustained for many hours below -42C for there to be an issue.
If the camper is well insulated, and continuously heated, condensation won't be an issue either. Fresh water and dealing with waste water will be the biggest problems I would think. And of course storage, particularly for bulky outerwear and boots.
