During the summer I normally shut off the dash AC and run the generator and roof unit. I'm getting close to 2000 hours on the generator being 8 years old and as second owner going on four years haven't done anything to it other than oil and air filter changes.
I think it's a wash between the dash and generator/roof AC concerning fuel usage when considering the additional load on the engine. Run the generator, stay current on recommended maintenance and enjoy the coach.
And I sitting back with a beverage and popcorn watching this one. Almost but not quite as good as a which chassis is better or tire pressure question.