[High On Octane]

Unfortunately there isn't much you can do about the paint on the inside.  Which frankly I think is estupido to paint the inside of a tank.

As far as the paint lifting around the fuel neck, yes vapors DO play a huge part of the paint peeling back.  What usually happens is the fuel splashes around the filler neck after you fill up and have a full tank.  All that paint that is on the inside of the filler neck then gets exposed to the fuel and starts to absorb it.  As the fuel is absorbed into the paint, the paint loses it's molecular bond to the metal and becomes soft.  Once it becomes soft, the fuel that is already soaked into the paint naturally turns into a vapor.  As the fuel vaporizes it starts to work itself between the paint and the metal of the tank, and the bubbling will get exponentially worse until you see the whole top side of your tank peeling, at which point a complete repaint will be required.  By cutting off the bad paint with the razor like you did, you are breaking the bridge between the introduction fuel to the paint.  With only bare metal at the fuel neck, the fuel has no way to contaminate the paint, unless you have a bad gasket.

Scottie J