I've never seen numbers published for Airstream.Hucho shows a few caravan Cds from the late 1950s in his first book.
Since the tow vehicle/trailer combination is what we're after,we'd have to have numbers normalized to some specific reference tow vehicle.And the composite Cd is based on the trailers frontal area.
For a clue about the Airstream,look at the radiused bus body of Cd 0.314,and then think about that Cd being lower,as it is partially shielded while drafting the tow vehicle.
The gap affects Cd
And if the tow vehicle is sufficiently large,the trailer drag can be cut in half.
It's complicated