Smaller Airstreams get reasonably good mileage pulled by diesel pickups.
One I like is the 19' Escape. It is big enough to be a functional RV with good size bed in back, decent convertible dinette in the front. Stove, conventional oven, microwave..decent stuff. Customizable during order to some degree-inverter extra batteries etc.
15 MPG towed at 60ish MPH on recent 1000 mile trip towed by Nissan Frontier 4.0. It was towed by a 4Runner previously and got 16 MPG towed conservatively.
If you really go small as in 13' Scamp, these will tow with some 4cyl cars and get over 20MPG. They''re fine as sleeping capsule.
