I wouldn't worry about the water heater. It's a large volume and it's already insulated. One cool night won't hurt it. (You could even turn it on, if you wanted). I would only worry about the lines. Or put a small heater in it if you have 110v available.
1988 Coleman Sequoia - popup (1987-2007)
2012 Roo19 - hybid (2012-2015)
2016 Mini Lite 2503S - tt (2015 - ???)
2011 Traverse LT, 3.6L, FWD
2009 Silverado Ext Cab, 5.3L, 4x4, 3.73
2016 Silverado 2500HD Dbl Cab, 6.0L 4x4, 4.10