It's the wind
you need to be careful about. A strong wind blowing on a part of the plumbing that is vulnerable to freeze-ups can quickly cause damage, even if the rest of the unit is toasty warm.
"wind freeze ups" -- https://www.google.com/search?q=wind...com&gws_rd=ssl
Recent post from Uncle Bob in another thread:
[click on orange arrow to go to this post]
Originally Posted by uncle_bob
How fast things cool down depends a lot on the wind. Some RV's have plumbing close to the outside "over here" and in others it's "over there". Get a good stiff breeze going from the "wrong" direction and you can indeed freeze pipes overnight with temperatures in the 28 to 30 degree range.
A shut down trailer rolling down the road at 60 MHP is very much a trailer in the wind. Usually daytime temperatures are well above the night temps. Usually we warm up the trailer when we pull over for the night. That's not *always* the case ......
Another issue is - where is the temperature being measured? If you are depending on the weather service, that may not have a lot to do with your campsite. If you are off in the deep woods by a lake, you may be at 35 when the weather guy thinks it's 25.(Been there / done that). Equally, if you are up on top of Mount Windy out in the wide open, you could be a bit colder than the weather guy. (done that as well ....).
People have lost pipes from a single night at 28 degrees (weather man temperature). Since most people don't carry a logging thermometer, it's rare to know what the real temperature was.
A chain is only as strong as its weakest link. In winter camping, the wind is often that weak link in the chain. For instance, the shower valve sitting on an exterior wall which is directly exposed to a cold wind.