Doesn't work for Interstates (this in the B-van forum). Airstream B-vans do not have a Zip-Dee awning; they have a Fiamma awning.
If you have an older Fiamma awning that doesn't auto-retract, you can use the Fiamma Privacy Room.
I have one, and use it sometimes— I'll be taking it to Farmington, New Mexico for the WBCCI International Rally because I'll be parked for 11 days straight and the extra enclosed space will help. But it's bulky to carry and takes long enough to set up that if I'll be camped less than a week in one spot I don't bother with it; I'll just add a sunshade hanging off the front edge of the awning instead.
Takes about 45 minutes for a single person to put up the Privacy Room, with the aid of a stepladder. First time takes longer because you have to install a couple of brackets on the awnings, but the brackets are permanent so they'll still be there for subsequent times.
At least that was my experience with mine. But I'm not terribly athletic— or well-coordinated— so it probably took me longer. and I'm sure it would go quicker with two people.
Good luck finding one these days, though. Fiamma doesn't sell them anymore; they were replaced by the Fiamma Privacy Room Light which weighs less, but sadly doesn't fit the 13-foot × 8-foot F65 awning on an Interstate (I checked; when the Light model came out I wanted one; the original model is heavy).
And if you've got a newer Interstate with the Fiamma F65 Eagle awning that auto-retracts in the wind, you can't use the Privacy Room at all; you need the model with legs to attach the walls to.