Hi Corinne and David,
My first inclination is to suspect that Overseas Caravan O-4 involved renting trailers and tow vehicles overseas rather than shipping personal Airstreams and tow vehicles to Europe, but I cannot prove it at the moment. It is entirely possible that the caravan participants put the caravan O-4 plaque on your 1966
Safari after returning home, even though that trailer was not used on that overseas caravan.
I say this because I know that WBCCI Overseas Caravan O-1 in 1973 did in fact use rented trailers and tow vehicles - I have talked to an actual participant from that caravan.
Actually, my hunch is that all WBCCI overseas caravans
used locally rented RV's (sometimes motorhomes in later years), although I believe that Airstream Company overseas caravans
were still shipping Airstreams and tow vehicles to Europe at least through Caravan 113 - European Adventure Winter 1977. I think the logistics of shipping Airstreams and tow vehicles overseas may have been more than the club wanted to take on, but Airstream company had been doing this since the mid-1950s, so they knew how to arrange it as economically as possible. It seems that after 1977 it either became economically prohibitive for even Airstream or else European trailing regulations evolved to the point that use of American trailers and tow vehicles became impossible without extensive retrofitting of mandated equipment (e.g. surge brakes instead of electric trailer brakes).
Next time I am in Jackson Center I will see if I can confirm my hunch regarding WBCCI sponsored overseas caravans using only locally rented RVs. I will also see if I can locate the caravan O-4 participant list, but without a WBCCI number from your trailer, I will not be able to pinpoint who may have owned your 1966
P.S. I spot checked a few WBCCI Membership Directories between 1966 and 1994 and did not find anyone with the last name of Gribble. That does not mean that Harold was not necessarily a member, because I did not check them all, but if he was a member, it was only for a very few years.