-18F is nothing to sneeze at, BTW. Anything below -10, and life or death ventilation issues start to get more difficult without a good heating and ventilation system, even with good clothing and blankets (after running out of propane, for example, due to inaccessible roads). When it gets cold enough, people in small spaces (like RVs) tend to make things too airtight—even more dangerous at higher altitudes.
When it’s cold enough, valves in common space heating and water heating systems tend to break and cause fires. Those need to be replaced with special systems made for such conditions in RVs (along with gobs of ugly insulation permanently on the *outsides* of RVs and temporary, insulated skirts for the undersides).
Without heat at more than ten below, one needs to be covered with enough layers (heavy stocking cap mandatory) and have a fail-safe breathing hole through blankets—a hole that won’t close during sleep. If several people are present, they can check on each other.
Good sanitation is really difficult in rough accommodations in extreme cold but must also be done. Sponge baths in air below freezing: not fun. Dishes and laundry become a real challenge. Lots of powder and extra socks are important along with the best tough, waterproof, insulated boots that one can obtain.
I cut leaks in boots that were probably a little too old during an emergency hike once, and had frostbite. After years, the feet still aren’t the same. Now, pac boots are checked before use, and there are backup boots.
I know it saved my life at least twice.
/johnny