My opinion, our fuel tanks rust from the outside because of the plastic cover...

[Ricko1966]

VW bugs. Gas tank,covered by the hood and vehicle belly pan below it. They rust out commonly.They rust from water in the tank. They also do not have a sealed fuel tank assembly as in basically the same as a vented gas tank.Condensation from the non sealed system contributes to the moisture problem.Gas evaporates , expands, vents and moisture and humidity from the atmosphere replaces the evaporated and burned fuel.Fix your evap. Systems people. And run a can of heet or alcohol blended fuel occasionally.

 

[C10MixMaster]

another area to watch out for is the back of the front fenders, the drain holes pack with leaves and mud holding moisture in there. my 99.99% Arizona rust free truck ended up with rust bubbles there. Every now and then i check to be sure the drain holes are clear.