Some of the Argosy trailers have the aluminum skin bonded to the frame work instead of riveted. The frame at the top where the sides and roof come together are made differently that the Airstream on the "square models".
We owned a new '87 Argosy 5th wheel with a slide-out--the trailer was first rate, but the slideout gave problems. We kept it for 3 years and got our money back when we sold it.
Some call the Argosy a "painted Airstream" or "square-stream".
Bill