They are called segment protectors and they can be purchased from Airstream or Out of Doors Mart. They show up on the Airstream e bay site from time to time with small blemishes but large discounts. As to weather it will fit your year I can't help.
Yes the bottom of the wrap area is black to match the newer trailers when Airtstrem started painting the roll black. I don't when that started but my 1976 was not painted originally but I did paint the roll black several years ago so that will not be a problem. I am looking in to the Segment Protectors as a finishing touch to polishing and new clear coat work I just had done at Oasis RV in Tucson. Scroll down to the bottom message with the most recent pictures from the thread below.