I took a different approach and I know this would not be acceptable to most, but -- I deleted anything that could freeze so I just don't have to worry about it.
We carry all our water in 5-gallon water containers carried in the tow vehicle. While in the travel mode our usage is about 2 gallons per day. So we carry 2 one gallon containers in the trailer. These are most often filled during the day at rest area drinking fountains (we taste the water first) and we also use a filter for water we drink or cook with.
Gray water is collected in a 2 1/2 gallon container via a hose from the sink drain and disposed of daily.
For hot water, we fill a kettle before we retire for the night. Then pop out of bed just long enough to start the burner below the kettle and pop back to bed. In about 5 - 10 minutes the kettle boils, the trailer is nice and warm and water is ready to make coffee. The excess goes into a large thermos to be used later.
We know this is not for most, but we'd much rather have this slight inconvenience than have to take all these precautions to avoid freezing pipes and appliances. Makes the
Scamp lighter on it's feet also.