From what I've found, the Toyota manufacturing facility in Georgetown, Kentucky is in a foreign trade zone, the U.S. version of international free trade zones. This one is specifically Foreign Trade Zone 29E.
That document lists the main benefits of a foreign trade zone, but they appear to be duty, tariff, and tax related.
Customs and Border Protection has a site with a great deal of information about foreign trade zones.
I didn't see anything specifying restrictions on firearms, but I wouldn't be surprised if there were such restrictions.
Hope this helps or at least gives you a start on further research.