Mileage is something you will hear all sorts of tails about and most of them stretched somewhat. The best we ever got was on I-90 with a strong tail wind. Lightly loaded 36 foot Itasca Horizon (2000) with a 300 Cat engine and a 5 speed Allison towing a Honda Element. Wind blew strong nearly all day and right up the rear of the coach. We got a bit over 9.5 and were very happy. Came across Oklahoma out of Texas one day in the same coach and had a strong head wind all day long. On flat ground the Allison would down shift on the little grades it was so strong. About 6.
I just count fuel costs as part of the price we pay for an expensive hobby. Can't NOT travel, it's too much fun and it don't look like fuel will get any cheaper in my lifetime.