I survived -20*F. Trailer has exposed belly/tanks and lines.
I had a hose on city connection that was traced with the Easy-Heat heat trace, then wrapped with foam insulation. The trace was purchased a little long, and covered the threads at the trailer, and also wrapped the stub out of the ground. The stub was wrapped with fiberglass insulation then a heavy plastic bag (to keep the insulation from getting wet). That also allowed me to get to the valve for shutoff while I was away.
Exposed gray and black tanks had stick on 120V tank heaters. Belly water lines were heat traced and wrapped as well.
Trailer was skirted with the thinnest OSB I could get, with 1" foam insulation on the inside. I had little flaps cut out to get to the drain valves. Sewer was hard piped and did not need to be heated.
This setup worked great for 2 winters.