>An insurance company is telling me that my fuel tank suddenly rusted out
>and caused the engine problems, because it was not run for about a month
>while parked.

The insurance company is out of its league. Of all the things that happen
'suddenly' on an automobile, 'rusting out' ain't one of them.

>When you store your Vanagon does your fuel tank rust out, requiring you
>to buy a new fuel tank every year?

I don't drive my van often in the winter, it just sits in the garage most
of the time with nothing special being done to it, other than keeping the
gas tank full. After several hundred thousand miles, I suppose it could
"suddenly rust through" but so far, no problems. :) Even in the summer,
the van has sometimes sat for 4 weeks without me giving it any thought.

There is an area on the top of the tank where water will collect and can
cause rusting on the tank that may eventually rust through, but that is
not a function of leaving the van sitting for a month.

John