With both my previous RV and my current RV, I ran a test. On both of them I did a 500 mile trip at 60mph. Then I did a substantially similar 500 mile trip at 70mph. Increasing my speed by 17% caused a fuel usage increase of 33%. My Class C went from 9mpg to 6mpg. My TT went from 12mpg to 8mpg. All numbers rounded to the closest integer. My personal speed limit when towing the TT is 62mph. (Most people drive on a 5mph division. To avoid wolfpacks, I drive 2 or 3mph off of a 5mph division. Everyone who is not passing me is being passed by me. No one drives along with me.)
