I don't worry about pipes freezing unless the temps are going to be consistently below 25degF - assuming you're going to be occupying it. There is enough residual heat which will keep the pipes warm enough.
Camped many times in 3 different campers in 25-35 degF weather and never had a pipe problem. If you're worried, turn the pump off, open all the faucets and open the low-water drains. This should let all the water out of the pipes - problem solved !!! (YMMV)
You may find that the tank valves may freeze