I'm not in a postion to comment of the item you opened up the thread for but the customs safe ports have been done in other areas I believe. I worked on a project up by Custer, between B'ham and Blaine, that was to be used by Canadian shippers. The trucks would come over the border with a seal on them, go to the 'safe' port and then out with being inspected or duty paid until the product reached it's destination. I really don't remember all the particulars as it's been 20 years ago. It had to do with paying duty on the products, inspections and the land used would be considered Canadian similar to embassy grounds.
Vague but that's all I remember.