Freezing propane tanks

I used to bulk carry propane but luckily forgot most of the esoteric math. What I do remember is sitting in my fish house out on the lake at -20f and we never had a propane or regulator issue. Some of our heaters approached 20K BTU or had supplies split for gas lights.

For an RV, the easiest protection for regulator freeze up would be a 5 sided cardboard box with a lamp inside, I'm thinking.