[sourdough]

As has been said, trying to reduce or eliminate propane usage in an RV with an enclosed, heated sub floor is ill advised. For me winter camping comes with the understanding that I'll be at the propane facility every few days filling a 30lb. tank - it just goes with the territory. Reduction/elimination of the heat under the floor (frozen/damaged water lines/tanks/drains) will lead to far worse, more costly problems (for you) than the expense of propane (for the renters). The use of a bulk tank may reduce the cost a bit, and certainly the time required for filling, but I wouldn't stop using it. On good days above freezing the use of a heating device would lessen the propane usage and still keep you comfortable. Also, a heated water hose is a must IMO in conditions like that.