There have been a few people that have had good luck filling the tank with Rust911 or Evaporust. As long as your tank hasn't been sealed previously and the sealer is failing or it leaks, you could do this without pulling the tank and be good for years to come.
https://www.rust911.com/ one gallon of concentrate makes 16 gallons so for $60 it might be worth a shot before you buy one from Berts and have it shipped cross country. That stuff also won't attack any terne plating that might be still in the tank.