I kept a 54' container just over the border that I would store parts in.When asked by customs why I was doing that I told them that storage was 1/3 of the price in a small town down there (true).
If you are planning to sell this stuff at swap meets in the U.S. perhaps you could keep it in a container south of the border. Load up on the way to a swap meet and bring back the stuff that didn't sell and put it back in storage.
That way you are not constantly explaining what you are doing to customs officials.
Just an idea..may or may not work for you based on your location.