http://www.pirithose.com/rv.php
We have wintered in the Wichita, Ks area once in an RV park. They strongly suggested how to wrap your water hose with 1.5' of heat tape per foot of hose. Then wrap with foam pipe insulation. That will work the real issue will be the hose bib itself and where it fastens on to the rig.
We did what Old-Biscuit suggested above. Filled on the weekends and used the RV park Showers to save water at our house. We also used and still do use this; http://www.thermocube.com/ to turn on light bulbs. Turns on at 35 deg. and off at 45 degrees. Was taken us through 3 winters both in a series of RV parks and travelling in cold weather. THE BEST advice is move the rig as soon as possible to warmer weather in the winter.