I have an Air-Ride big enough for my Trikes and to be honest, I never give a crap about mileage.
I can tell ya one thing, my Big Ram with a Hemi averaged 13.7 MPG over 12,000 miles. That was towing and not towing. The highest MPG I got was 15.9 on one tank and the lowest was 9.6. 9.6 was when I was high balling it for Vegas.
My Dakota with the Mercedes engine (V-8), overall for 17,000+ is 14.9. Highest was or is 25.6 and lowest was 9.1.
Neither of these 2 vehicles have been babied. I drive them just like I ride the Chevy Trike or the Valkyrie Trike, Balls to the wall.

This trailer is all air suspension. You twist a valve and the deck lays on the ground. Ride on and set the front tire in the chock, step off and put the 4 straps on it and while doing that turn the air valve and it will rise to traveling mode. Sure beats all the ramps I have used in the past. It you can see straight, you can not miss the lowered deck.