Fuel (diesel) mileage for my 2018 Melbourne 24L averages 13.5 MPG and 11.5 MPG while towing a 2014 Honda CRV. This is for predominantly highway driving around 64 MPH. How does your fuel mileage compare?
I think there are a number of "what mileage" threads out there and my thought is I don't care to look and don't worry about it. If you are worrying about your fuel mileage you probably need to sell the RV and find something else to do. They were not made to give you great fuel mileage.
I do clear the trip odometer when I fill and if I would look at it down the road and without wind, hills and other factors see it out of the ordinary I would get "slightly" concerned and check.
I headed out on a trip in mid April towing a CRV for the first time. I am not overly concerned about fuel, but was curious about the impact of flat towing on fuel mileage. Today I disconnected the CRV and noted the improved fuel mileage.