Many RVs have poorly insulated floors and the heat that escapes will be held in by the skirting system, helping to keep your pipes from freezing. With many newer RVs with 4 season packages and insulated underbellies, you don’t have this incidental benefit. If you have one of these, or are camping in freezing temps for extended periods, it’s wise to use a supplemental heat source under your RV.
Never use anything with an open flame, or that can cause a spark, and always closely monitor the temperature and conditions under your RV.