[Chief of the 60's]

Still a Unibody vehicle with sheetmetal frame rails and dragging tail. Its got a load on it.

Also, Airstreams are very well built and not necessarily that light.

The average weight of an Airstream trailer is 2,500-10,000 pounds:
•Classic: 7,788 lbs.
•Globetrotter: 5,297 lbs.
•International Serenity: 4,761 lbs.
•Flying Cloud: 3,852 lbs.
•Caravel: 3,200 lbs.
•Bambi: 2,900 lbs.
•Nest: 3,400 lbs.
•Basecamp: 2,585 lbs.