I just did a 2400+ mile winter trip (early December 2021) with my 550 + 1970 IH Scout tow vehicle, which included crossing the rocky mountains twice. I have an electric ceramic heater (which worked well), although after high recommendations from several friends in the colder area's, I purchased a Little Buddy in case of emergency.
During my trip, frequently experienced night time temperatures from 0 to 10 F, but between the body heat generated from (2) people, my Camp Inn heated up well, and the ceramic heater was the "cherry on top". I'd like to think that the ceramic heater helped some with the humidity generated by two adults, but that is an ever on going issue.
I would not have ever left the little buddy running un-attended and/or while we were asleep, but in an emergency situation I definitely would have used it.