POR15 is excellent. I’m not usually swayed by celebrity endorsements, but Jay Leno states that he (or rather, his staff) uses POR15 in restoring all of their high-end vintage cars and bikes.
I used it on Lucille’s tank and works precisely as advertised and it reportedly can seal minor leaks.
When I used the pre-treatment wash - the water came out looking like bad coffee with lots of grainy rust. after several rinses, the interior was a relatively smooth steely coloured surface. Then, as WW said, after it dried, I used the POR sealer compound and then after three hours of laborious tank-turning - it was done!
The only casualty was my two arms from the continuous turning - my shoulders felt like they were going to die.
Pete