I got some info from a friend a while ago when DW and I considered some winter camping. We never ended up camping because DW decided SHE didn't want to be in the cold for a long time. Here's some links:
http://plumbing.hardwarestore.com/52-299-heat-tape.aspx (example products)
http://www.ehow.com/how_2097799_cold...r-camp-rv.html (RV how tos)
http://www.nofreezewaterhose.com/ (military grade, expensive heated hose)
An internet search might yield more and there will be plenty of experienced cold-weather campers to help out soon.