Originally Posted by Goatboy
The trailer serial number of 5031 decodes to a 1949 18' Trailwind, which was produced in smaller quantities than the more common 22' Liner. I do not believe we have any information to know how many were actually made, nor how many have survived. It is definitely one of the rarer models, but not unique.
There is no way to trace any of the history from the serial number. Your main hope for that type of information would be the current seller or the previous eBay seller. Have you tried calling the eBay seller via phone since his number is in the eBay ad and not just trying to reach him via email? He also seemed to provide detail of the restoration (which I believe he actually did himself) in the eBay ad. He would be the only one who could provide more detail on that.
If there were ghost outlines of old "big red numbers" (i.e. Wally Byam Caravan Club membership numbers) on the front and back, those could be looked up and guesses made about prior owners and where they lived, but given that the Trailwind has been polished, evidence of such numbers (if ever present) may have been removed or may be very hard to see.
Bottom line, your best bet is to make contact with the recent sellers and see what evidence they have of prior ownership.