Install a vent in your fuel can ? Atwood tank, Honda 2000i

I have an atwood boat tank like that. They let air in, but not out. And they do
swell up big time in the sun. I used the smallet drill bit I had and drilled
a hole right through the center of the cap. Problem solved. I didn't need 6 gallons of gas all over the boat. But...my boat is garage kept, even though
I don't think it would let much water in.
Brian