Gas Station

I know it's a hassle but I would put a ball valve on each vent for 2 reasons.
Closing the vent prevents gassing off. not so much the diesel but the gasoline will gass off quickly.
it keeps the moisture out as temperatures change humidity gathers in the open atmosphere of the tank and gets locked in.
also if there happens to be a failure in the delivery system it would hinder the flow.
Yes, you would have to remember to open and close the valve, but it is also a guard against theft in the event someone thought to steal and not knowing how to operate the system.
An ounce of prevention.

 

They make 2 way atmospheric valves, One to let off the pressure and one that will let in atmospheric pressure in the event a vacuum forms in the tank