Using something like vinegar really invites pinholes as it eats all metal as well as rust...evaporust type products only chelate the rust which doesn't impact any good metal. Not that pinholes aren't possible. A liner on a tank with more than light rust is generally a good idea I think and agree with HondaMan, POR or Caswell's are the best liners I think. POR being very picky about prep...
You must be sure it is dried out extremely well, you do not want to capture water/moisture under a liner.