Okay - been there, done that. I do dioramas professionally, and have shipped them all around the world (Germany, Hong Kong, Australia, Canada, and England at least!). Here is my method... it *usually* works pretty well, but there is not a guarantee that EVERYTHING will make it there in one piece:
1) Build a CRATE (wood is required!) that will allow for 6 inches of space all around the dio.
2) Place newspaper in the bottom of the crate.
3) CAREFULLY, place your finished dio in a garbage bag (I prefer clear bags for vision).
4) Spray a can of "self expanding" foam into the bottom of the crate on the paper.
5) Before the foam is fully expanded, set you bagged diorama into the foam.
6) Wait 10 minutes for the foam to finish expanding.
7) Now spray additional cans around the sides and top of the dio bag. Leave just a bit of room as you don't want the foam to actually expand to the point it crushes your diorama!
8) Wait 24 hours for the foam to form a hardened shell
9) Add in styro peanuts to fill in any last remaining gaps
0) Seal the crate, bring it to a quality shipper (I use DHL) and PRAY!
When the unit arrives state-side, open the crate, and you will find that you can then break off the hard shell of the now dry foam. The plastic bag will make it come off easily. Start at the top and work your way down, trying not to break off huge pieces, as these could accidentally press against your diorama.
I once shipped a piece with over 60 figures pinned to a base - my customer told me that not a single figure had been broken off in transit!
