I have not tried a similar situation, but probably will next spring. We specifically bought and set up the A122 for 3-season long weekend camping in the Colorado Rockies without hookups.
The extra battery was put in to carry the heater for the long weekend.
As far as water freezing, based on my experience at my house (7600 ft), I doubt it's going to freeze hard or long enough to do damage with the lows in the mid-20s (assumes highs in the mid 40s). Where the sprinkler lines are above ground (and before I blow them out for winter in mid-October, or after I fill them in the spring at beginning of May), I've only once had damage with the lines freezing.
I do not winterize since I keep the A122 in an unheated, but insulated garage. I have seen garage temps in the mid 30s - the slush on the car takes a long time to melt.
I am convinced (but may yet be proven wrong) that the running heater (interior around 55), water heater, and the normal Colorado sun will be sufficient to keep water tank and water lines from freezing hard.
just my experiences to date