Previous experience with campers, it takes very, very little water in the wrong place to freeze and break a cheap plastic fitting. While the fitting may be inexpensive, the resulting damage and clean up can get expensive. I always blow the lines, drain the water heater, leave the low drains open (leave the caps off on this one, going to switch to valves) and pour some RV antifreeze in the drain traps. Freezing water can do an amazing amount of damage in the right places. I have seen schedule 40 iron pipe freeze and split.
Our camper stays plugged in when at home, currently it is parked right behind the house. Next year we should be getting a new large barn built, then it can be parked inside completely out of the weather.
Aaron