Download this Onan .pdf document on their 4000 watt RV generators and scroll down to Page 2. Notice down near the bottom of that page that this size gas Onan generator consumes around 0.5 gallons per hour when loaded to one-half of it's capacity:
https://powersuite.cummins.com/PS5/PS5Content/SiteContent/en/Binary_Asset/pdf/Consumer/specsheets/a-1399.pdfI figure that our RV's 13.5K BTU air conditioner loads our 4000 watt Onan generator to 40%-45%, which means that it will run between 2 and 2 1/2 hours on a gallon of gas. I agree on a built-in generator being "worth it's weight in gold" at times when nothing else will do. After all the $$$ we spent on an RV, we want it to be able to keep us comfortable at any place at any time. We can't always predict what camping situation we might wind up in, so why not be ready.
Also for what it's worth, with a convenient built-in generator in the RV the entire RV can be run as "all-electric" in an emergency with no hookups if ever required. For instance, if the propane system should ever fail the Onan could provide the power for heating the RV, the power for cooking food, and the power for heating water. :C
