I just started watching Season 4 on DVD last night and was thrilled to see the Airstream, though it is a shame that Unser isn't doing too well.
Looks like an early 70's model to me. Maybe a 71 or 72, mid to high 20's in length with a rear bath. The overall condition isn't too bad, though he could clean up his camp a little.
The gun rack in the front window was a nice touch though I prefer something more low key, such as a .357 on the credenza, hidden under what looks like a carelessly discarded t-shirt.