Generator on for Ac while traveling

JMO , for Us it is all dependant on outdoor temperature and how many occupants , in good weather the coach AC is sufficient in the front two seats or making a sandwich but if it's 90 degrees you will have little choice but to burn the fuel and run the roof top units via Generator,and maybe then if cooled out you can turn off the coach AC to compromise on load on the engine vs the generator running to somewhat equalize fuel useage. I would estimate a diesel genset near capacity using around 3/4 to 1 GPH
Bottom line we bought Class A's for comfort not MPG so enjoy yourselves while riding too .