With my three class a's I have always ran the gen.,I start the motor then start the gen. unplug and off I go.
The reason for me makes sense. The coach stays cool all the time, this way once stopped with no dash air the coach is already cool. I also like to keep the frig running on 120v with the gen. running my frig stays cold also. When stopping and want something warmed up to eat in the microwave its ready to go. Generators are made to run the little fuel they use to me is not worth it. But then I am not concerned about my fuel mileage. I have the coach to use if I get 5mpg or 50 mpg I am going to use the coach.
Enjoy