Hi, Cowgirl, and welcome to the forums. I took the liberty of moving your post to its own thread.
there are people who frequent the site who can probably decipher that number, or help you find the serial number if thats not it....but I am not intimately familiar with the '50's trailers. Some of these individuals might be at the Wbcci International Rally this week, and may have limited access to the 'net, so they might not see your question right away.
In the mean time, I did find this document from the Vintage Airstream Club's website, which is a catalog from 1955
. perhaps you can match up your trailer to one in this document: