Fred and other experts -- so why did Airstream change from 13 panel to 7 panel end caps? The change was in 1957 - right? So does that mean, other than this mysterious 1960 13-panel trailer, that anything 1958 onward should have 7 panels? someone mentioned "dog legs" in the early 7 panels. What do you mean? Thx Marg in Pac NW