Good news! As of today, the coins are being moved indoors. They only stayed in the garage for a few months and most of the time was summer. I'm sending them some gel packets to try to absorb any moisture they might've picked up. Otherwise, they should be safer than they were. Thank you all for your input!
Yeah, I agree. I wouldn't worry about the little air that might get in over time. This little air and contaminates are a lot less of a threat than all the air that could get in a less airtight container. Nothing is airtight (as far as I know), so it's about minimizing harm.
Just as a side note and in addition to Gel Packets, I have this at the bottom of my safe. Not sure if it helps but it can't hurt.