Do you now who you sold it to? That's the logical place to start.
You can do a search of the Airforums members for a 1965 Caravel
and see if that gives you any leads..I just did it and got 3 pages of hits...
To do a search, use the pull down "Quick Links" tab in the lower right of the header banner at the top of the page..and click "Member Search"... then enter "1965 17' Caravel" in the search parameters under "Trailer #1" and go to the bottom of the page and click the "Search Now" button. You can do the same thing under the "Trailer #2" parameter for a different list.
You can contact members through a "Private Message" (PM) with the VIN number or ask them if they might be the current owner of you family's old trailer...
Good luck tracking it down! It could be anywhere!