Gas filler neck to gas tank seal

I just purchased a new fill tube to gas tank seal for the 72 Dart part#3404182. It looks a little different than the original. On the new one there seems to be one side with more rubber like a double seal. The parts guy said it was like an additional dust seal they added but I'm wondering if that side should be in the tank or outside the tank as the parts guy suggested with his dust seal comment.

Any installation tips as far as what side goes in tank?

I'm thinking the double seal side goes in the tank shown on the bottom of picture. The part number is on the top side of the seal in the picture I would think that would typically be visible when installed. Probably work fine either way this stuff just bugs me when I don't know for sure.