Hi Bud,
We purchased our Southwind in 2017 in western Canada and drove it back to Ontario (approx. 2500 miles).
The RV was visually empty during the trip other than fuel and some fresh water.
During that trip I was getting just over 9 mpg (US).
Once we got home and started loading in all the items we would normally carry on board the mileage dropped to 8 mpg.
This mileage has been consistent during travels to Florida each year and includes driving through the mountains.