Hi Aage!
I know Rich Luhr the editor of Airstream Life blogged about and included pictures of new windows being put in his Airstream at Roger Williams Airstream dealer in Texas. Here is his blog, I cannot find the specific entry right now unfortunately.
Tour of America You'll have to look back in the archives. He had a wide window and an overhead vista view window installed.
I also read that Colonial Airstream of New Jersey put in a wide window in one of the new Safari Sport models.
Perhaps you can get more information from them on the installation.