As mentioned above the big things for my Ram 6.4 hemi and 27ft Lance are wind, speed and hills. I range from about 8 to 10. When we first started RVing after retiring in 2010 I worried and sweated about getting the best mileage I could...I got over it. I drive between 55 and 65 mph most of the time.
My normal response to people now who ask about what mileage I get is "I get between F and E. When it drops to E I just add gas and then I am back at F!
As for speed, my wife and I don't make reservations and most of the time don't know exactly where we are going so what sense would it make to drive fast to get there.