For freezing overnight temps, the above ideas are great. The sealed underbelly does help. Here are 3 recommendations that come to mind for freezing temps:
1. If you have the "Arctic Package" or something similar, turn on the tank heaters and leave them on. They are like a heating pad and I don't think they can get too hot or burn out like the electric element in the water heater.
2. Use your fresh water tank and pump and only connect to the site's spigot to fill the fresh water tank. A frozen fresh water hose in the AM is the most likely thing to freeze overnight.
3. If possible, use something like an electric water pipe heater wrapped near your tank valves. Again, this won't burn out or cook your drain pipes but will leave the liquid in liquid state as opposed to a solid.
2017 Forest River Surveyor 247BHDS...
...Tugged by a 2016 F250 XLT FX4 SuperCrew, Shortbed 6.2L, 4wd, 3.73...
...Joined with a Husky Centerline TS 800-1200lbs WDH