Once the rust has started it'll continue. Just keeping gas in the tank won't stop it so you'll either need to coat it or replace it. While I've had excellent experiences using coatings, it is expensive & has to be done right or it can fail. If a new tank is available for your truck, that would probably be the best way to go. Short term you can probably get by with not doing anything but putting a good inline filter on the gas line to stop any particles from getting into the carb. Eventually you'll need to address the issue though.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.