Evapo-Rust. Removes rust, leaves phosphoric coating.
Caswells tank sealer. Seals Tank.
Repair the pin hole with silver solder. (hard solder)
Surface rust will appear on ANY bare metal surface where moisture is present, such as gasoline from the pump where ethanol has been added. (Unless you live where I live, where it's dry as a bone, and nothing rusts, ever, except my joints)