No one has mentioned, probably partly because there are almost
no air-cooled Vanagon folks here, but my observations,
owning both an air-cooled and a (former) water-boxer, is
that the air-cooled never had seam rust problems.  They had
surface spots--measles--but not seam rust.  The water boxers
had good surface paint, never the measles, but they had
seam rust.

Richard