My experience is limited. My MGB tank was corroded but only where water/condensation collected at the lowest point. This was around the pick up, and along the front edge. I treated that going in through the sender hole using a long brush, and a rust converter.
Someone in the club tried to vacuum the rust out, and it exploded the vacuum when the motor sparked the vapour. Tanks are dangerous. Even draining one leaves residual vapour outside and inside. It's suggested that you can pump exhaust gas through the tank to neutralise vapour, but I've never tried it.
A corroded tank will never stop presenting problems. But first, find a way to look inside.
