In use or just stored? Most winterized RVs will have a rating to how cold they can stand but there are a lot of variables. In a Class A, many have insulated and heated wet bays but if you use alternate heat from the forced air furnace you may short change the wet bay heat. Wind can also have a chilling effect, stealing heat faster than it can be replaced. Keeping windows covered with insulating curtains can help, but condensation can build up and cause water damage or mold issues.
Another factor is of course how cold and how long? A night of below freezing temperatures are not a big deal, but sustained temperatures in the 20º or lower might create problems. Leave cabinet and closet doors open and even help the air circulation with a small fan or two. Putting incandescent light bulbs (120 v) in the wet bay along with wireless remote thermometers to monitor.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI