Jbrowning
I've had trailers just like yours with water tanks and lines inside. I prefer that in freezing temps. The water will freeze where it goes under the doors in really cold temps. Loosen up the straps that hold the water lines down to the floor or wall to create an air barrier under them.
I use vinyl skirting without insulation combined with a light bulb under the holding tanks takes you down to around 8 degrees without freezing. I use two lights directly under tanks.
Having said all that and spent years in an rv through Idaho winters, now I blow out the water lines and winterize and bring water and set a porta-potti in the bathroom.. Much easier without ever having to worry about freezing.
I have spent many a morning with hair dryer in hand trying to thaw out water lines and figuring out where it froze or outside shaking water lines and pouring hot water on connections.
By winterizing and using a porta-potti there is know worry of freezing, hooked up to power or not, using water jugs/paper plates and a catalytic heater to keep you toasty warm.
