"Any idea" would be some time in the 60s. Our 1960 Pacer had "rope and pole" (we adapted an awning made for a pop-up camper) but I have seen mid-60s models with Zip-Dee awnings. Of course, they could have been added later.
According to the Airstream Life magazine about 1965 Airstreams
"The new unitized rear-entry door swung towards the center of the trailer and easily accommodated a permanently mounted awning, an accessory that was becoming more popular than the put-up-and-take-down canvas rope and pole awnings of earlier years."