I agree that it's pretty close to a wash in expense, My gas generator manual states that it uses .6 gal/hr vs. what the engine would use powering the dash unit. I resisted using the generator until we took a trip thru the Rockies in very hot weather. The dash air would not cool the coach very well and I didn't want to give up horsepower running it going over the mountains. I started using the generator/house air and very quickly came to enjoy the improved cooling. I doubt if it would make much difference in expense...and when you're talking about how much it costs to run one of these it seems like a drop in the bucket.
2004 37B Adventurer, 8.1 WH, Ultrapower, DIY CAI, Henderson Track Bar, Tru Center, Koni FSD's, Roadmaster Even Brake, Scan Guage II, 180 Thermostat,