[jimcol]

All your plumbing runs through the underbelly of your RV. Between the coroplast you see from the ground and the bottom of your floor you see from inside your unit. The only way to get heat into the underbelly is by running your propane furnace. The furnace has a flex duct that dumps heat into this area. Thats the best method to protect your pipes and holding tanks. Some have placed a remote sensor in the belly with a temp display inside their unit to get a feel for how quickly the outside temperature affects the temps in the underbelly.