Greetings, Nancy! And Congratulations!
Although there was no Owners Manual in 1958, there were brochures and sales literature which may be of interest. Some of these are available online at the VAC site.
Check out
www.airstream.net/members/documents/index.html
The '58 is not represented, but the surrounding years may be useful.
Also, the VAC publishes a quarterly magazine called the Vintage Advantage. The current issue has a comprehensive article about the Airstreams of the early 50's. I believe that the next issue will focus on the late 50's, so you might look for that.
Finally, there will be a VAC Vintage Rally in your neck of the woods (Duncans Mills-Russian River) in early October. Although the rally is filled, you might be interested in the open house on saturday, Oct 11.
In any case, Welcome, and smooth sailing!