There's no easy answer. Conditions vary by climate and by RV.
It was 27° when I hitched up at 6:30 this morning. It was chilly enough indoors that I didn't want to get up. Once I got moving though, I couldn't believe how cold, sluggish, and crunchy everything was in my pickup while all my tools and accessories were toasty warm and pliable in my storage bays. The ducting for our furnace is good, but not great, which means that the basement stays pretty warm.
Ditto for the cupboards. It was nice and warm when I opened the cupboards under the bathroom and kitchen sinks.
So for us, a few nights where the overnight temps dipped into the 20s with 45° daytime highs worked out just fine. I wouldn't chance it if it were much colder though.
