Spent 2 winters in northern Nevada (-20*F). My trailer is an exposed belly, no frills unit.
I used pressured water from the spigot. I added the 'Easy Heat' heat tape to my water hose, and held in place with electrical tape. The t-stat was placed about a foot from the trailer end, went to the trailer city connection and wrapped around the 90* fitting, then back along the hose to the spigot. Had ordered enough to give me a couple feet at the spigot to wrap around the valve and line in to the ground. Hose was then covered with foam insulation, and fiberglassed the water connection and wrapped with a plastic trash bag.
I used a stick on holding tank heater to the gray and black tanks from Ultra Heat. 120VAC only for me. I drained only when tanks were full, to keep from possibly icing my drain line.
Whole trailer was skirted with the thinnest OSB I could find, and was backed with 1" foil lined styrofoam insulation.
I also installed the styrofoam in the windows and entry door, cut to fit, and wrapped the edges with duct tape to keep the foam balls from being everywhere.
I also swapped out the single power outlet for a dual unit on the back side of the fridge, plugged in a low wattage bulb and covered a majority of the fridge vents to keep it working properly.
I survived.
2005 2500 Cummins/48RE/3.73, QCLB, 4wd, BigHorn, Edge Juice w/ CTS + Turbo Timer,Transgo Shift Kit ISSPro Oil and LP pressure gauges, GDP 20/2 filters, Custom Diesel Steering Box Brace
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Honda EU3000I Genny