Banzaibird

First you need to get in touch with the proof house, Liege, Ferlach, Birmingham wherever and find out the rules and paper work needed to have the rifle imported into that country. they will help you or put you in touch with a company over there that will.

I have just taken the rifles in question over, to Liege, on a cheap flight and avoided most of the paperwork, here and abroad. You will still need some importation documents in Holland but not in Belgium if you travel by train. If you send it, use Benelux and it will go directly to Brussels where an agent will clear the paper work.

If arranged prior to your trip they will do it on the day you want, it is a one day process and, in Liege, you can also get the barrels regulated at the same time if that is a problem. You will only be getting the final proof if the rifle is done, not the preliminary ones.

If it blows up you won't have to worry about importing back to the US

If not all you will need is the normal Customs form, that you owned the rifle before you left.

I know rifles are sent from Aus to England regularly for reproofing and refinishing so some else can give you that.