I have a 2003 Designer and have camped to 17 degrees, the high the next day was 34 and back to 20 that night without any issues. Did go through a lot of propane! Disconnected the water supply and ran off the pump. When ran out of water, refilled the tank. I left grey tank valves open and held blackwater.
In February of this year we were out and had below freezing temps for 9 consecutive nights including 5 inches of snow. See photo's on my profile.
F250 HD 7.3 Diesel :)
31 Ft RLS Designer 5th Wheel :D