Can I use the rust sealer in a gas tank that has baffles?

Yes. Etch with Metal Prep first, and use an engine cleaning gun to spray the Slim rust sealer into the tank when the Metal Prep has dried thoroughly. Be careful not to spray too much/too heavy. You can slosh the rust sealer, but it’s important to stand the tank on end until every last excess drop of rust sealer has dripped back out or it could harm the baffles.