Thanks for your response, karne. For your interest we are currently in eastern Montana headed for Williston, North Dakota where the current temperature at 4:00 PM is -22degrees Celsius. When we made our last trip to Nationals in 2008, they had to drain the water from our sleeper car so that it would not freeze up. As I recall temperature overnight at that time was -30 degrees Fahrenheit which would be about -34 degrees Celsius.