I was afraid it would get moldy in that tin body of yours.
Although vitamin E is a good preservative and definitely good for your dog, I don't think that's the answer for keeping your treats from turning moldy.
The paper bag also allows air to pass through, preventing buildup of too much moisture which can cause the seeds to go moldy.
Mold problems may be visible or you might suspect a hidden mold problem if a room smells moldy.
If you prefer the moldy oldy treatment, something perhaps a little more Goth in nature, how about an old skull lying at the base of a tombstone?