The OP stated that this is a non selling show. All the works I have loaned were for the same — some shows/exhibitions were dedicated to one artist or others to a particular theme or subject so the works were there just for the show.

What surprised me about the original post was that no professional shipping was involved for the UK gallery show— as the UK has an import duty on art; the duty is paid when art is sold unless it is exported from UK.

The customs issue is very complicated which is why even when carrying something by hand (only done twice and for small works on paper that fit in carry on) I have paid for a customs broker. I did not want to have any problems with customs. Some people have done the Carnet themselves but I did not want to make a mess of it.

If I buy something overseas and have it shipped to US I am send a copy of entry paperwork.