Approximate fuel milage of these 2 motorhomes?l

If I could have found a handicap diesel coach that is what my gasser we have today would be. Diesel chassis just seem to ride and handle better to me.
Long distance traveling, give me a diesel any day.
We have crossed the country several times in a diesel and mileage varied. Had a 300 Cat engine and on one trip across, east to west, we got great mileage 12+ . Same coach, engine same towed we got just a bit better than 5. Difference? We drove into a strong headwind all day long.