Using 1/2 gallon per hour will get you pretty close. If you want to get closer you can figure out your coach MPG when not running the generator and your next outting, fill up before and after and see how much your MPG is reduced. The difference is generator usage (again, close).
If you have a 50 amp connection to your coach at the power pole you would not run the generator at all. If you are connected to a 30amp power pole you may still be able to run both A/C units if you ensure everything else is off. If you are just connected to 15/20 amp circuit you coach should have an automatic transfer switch and the generator always gets priority. As soon as the genny starts producing power, you will be disconnected from shore power.
