Please note: if you are driving the truck/vehicle infrequently, air in the gas tank will contribute to the (rapid) deterioration of the ethanol fuel in your tank. Everything I've read and my personal experience says the fuel will start to go bad between 1 and 2 months of storage. You can see a post of mine about a month ago showing 3 vials of gas...one new and 2 which had been kept either in a new gas tank or a plastic lawn mower storage tank...and the results are not pretty. So you might not want to vent the thing too greatly. It actually does not take much of a vent to allow a tank to work. You're not consuming fuel like a blown dragster, after all.

~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end