We have a freeze warning here in the foothills of Northern California so I was concerned about my motorhome. A 2006 Itasca Sunova 26P Class A. It is supposed to drop down to 26 or 27 tonight and tomorrow night. Highs during the day will be 43-47. I plan to take my RV out soon so did not want to do a full winterizing routine on it, especially since living here in California we don’t get the long periods of freeze like they do in Illinois or other states. So I did a little research on google.
One benchmark I read was not to worry about it if the average daily temp is >32 (some say >=35). So for example if the high was 43 and the low was 27, no problem. I also read that unless its prolonged freezing weather, ie greater than 24 hours straight, there would be no worries down to 25-27 degrees. Some give a guideline of no lower than 28 and at least a day high of 45 for an unheated RV. These are general guidelines and common sense should prevail. For example high wind could add to the freezing potential and length of time at continuous freezing temps.
Also its best to have the water tank at least about 1/2 full or more since the bottom water will stay warm enough to not freeze. (Contrary to my thoughts of draining it.) Also, if possible, keep it warm inside the vehicle with the heater running, or light bulbs and open the lower cabinets to let that warmth inside the plumbing. I will keep my hot water on all night since that tank is only 6 gallons and it’s plugged into the house and has an electric alternative. Another extra safety is to add some RV anti-freeze to the black and grey tanks. And the toilet bowl if there is no heat in the vehicle.
I have installed Reflectix on some of the windows and I noticed there is also some in the fresh water and water pump area which will helps. 
So tonight and tomorrow night I will set the thermostat of the motorhome to about 54 inside, keep the hot water heater on all night, fill the water tank half full, leave the water pump on, put some anti-freeze in the p-traps and toilet, and cover the windows.
