What is a furnace? What is freezing temperature?
Here we are at a latitude almost the same as Denver & we are aleeping with windows open & bedsheets. No blankets needed. Night temps in the mid 60s.
We seldom need the use of our 5er's furnace, usually getting along just fine with the built in electric ones.
Had our share of miscellaneous problems though & it is always good to have the part handy, be able to self fix, or find what is needed right away & not far away. Many miles, many nights, many years & the trailer has not been to a repair facility yet for anything inside 'the house' part.