After years and years of laying up my MG's I concluded that a full tank was the best fix, limiting the amount of air in contact with the fuel. The only time I had fuel go off was when I left a couple of gallons in the tank, and it really did go off in a big way. The smell was strange, the car wouldn't start and the fuel lines were coated with a green waxy deposit. For the last few years of MG motoring I added fuel preserver to the full tank.
The other effect was that condensation gathered at the lowest point - water being heavier than petrol, and the tank corroded around the pick up and along the leading edge of the tank - the lowest points. Everywhere else in the tank was pristine - viewed with a torch through the sender hole.
