The problem is that the boiler can run dry if you are to far off level and leave it running. While driving, normally the refrigerator is bouncing around enough to get the ammonia and water mixture back into the boiler.
Parked is another situation. So is driving slowly through a construction zone. One Rv. Net member had a fairly new RV, and took it on a 3 hour drive, with about 1 hour spent in stop and go traffic on a hill, due to repavement project. Once at the campground, the refrigerator did not work, so they wisely shut it off, and did not use it. Once back home, he plugged in and it worked perfectly, so he asked why?
Once the boiler is dry, any remaining ammonia can turn to powder, and clog the orifices. The drive back home with it off unclogged those orifices, and everything works fine now.
So yes it is best to shut it off while shopping for a few minutes, especially while buying fuel, (flame and gasoline vapors!) and through construction zones as well, if you will be stuck moving slowly for more than about 10 minutes.
Have fun camping!
Fred.