my best MPG was coming east across eastern WY and nebraska last summer. tail wind 20-30mph. i wanted to put up as much canvas as i could, but didn't have any
. for about 500 miles i did 10.9. traveling 60-62 MPH (i find that is my sweet spot speed for best mileage). also tires 100 PSI cold all around (they run 110-118psi ish going down the road, depending on outside temps). jeep behind.
worst mileage was also last summer, on the outbound of the same trip. coming west across ND and into eastern MT. a starboard quartering wind that would alternative to dead on the bow. gusting to 30-40 at times. really glad i had the roadmaster front and rear track bars. if i had the sumo springs also they would have helped for sure. when the wind would switch back and forth in direction, the coach would move alot, but never felt unsafe. but it was always two hands on the wheel and very focused driving; the most tiring 450 or so miles i have ever driven in any vehicle, bar none. the rest areas and exit ramps were full of semi's and coaches pulled over, resting, waiting for it to stop. barely a cloud in the sky, of course, and i needed to get to portland, OR on time, so i had to go unless it was totally impassable. on the ponds and lakes out there, there were white caps, it was blowing so hard. mileage you ask ? 4.1mph. due to conditions, slowed down to more like 50-55, and had the jeep behind. again tires 100PSI cold.
my average is around 6.8-7mpg around here in new england. did the run from CT to southwest harbor, ME this summer and averaged 5.8, but i had the genset on the whole time running both AC's. that would account for about a 1mpg, best guess.
from my many, many, many conversations with non exaggerating pusher owners of roughly the same size as our setup, they get about 25% better mileage in all conditions. like has been said, you don't buy the pusher for the mileage, it's all the other reasons. if you want mileage, buy a class B diesel puller. but that's apples and oranges.