My fuel mileage depended on factors such as speed, wind and terrain. If I had level ground and not fighting a headwind and driving 60 mph I would get 9 or 10 mpg. When I got into mountains of Kentucky and Tennessee my mileage dropped to 8 mpg.
When I wasn't pulling the Windjammer, which was 90% of the time, I averaged 14.5 mpg.
Your mileage may be lower when towing than mine was but I know you get better than 14.5 in everyday driving.
Hope this answered your question.
Steve & Lauren
2011 Windjammer 3065W
2012 Ram 3500, 6.7 Cummins