I've packed many containers in many countries, including a couple of
glider shipments, and never heard of pulling the contents out of its
box to ship. Everything has a schedule B number on the Shippers Export
Declaration but can be shipped together. Try looking these up, as they
may have changed.
Glider 8801100060
Trailer 8716400000
You'll find that information for one form doesn't mean anything on
another form, and discover bits of the bureaucracy that you never
imagined. My favorite was BIS - the Bureau of Industry and Security.
Probably about to be phased out until they added the word Security.
Should just eliminate the Industry and call it BS.
If this is a permanent move, you must de-register the glider with
FAA who will send the document to the similar agency (EASA) at the
other end.
If shipping overseas temporarily, you may want to use a Carnet, which
is essentially a bonded passport for equipment.
Jim