On Fri, 20 Feb 2009 07:48:18 -0800 (PST), "Hustlin' Hank"
wrote:

In addition to what the other posters have said, you may have it too
tightly sealed also, therefore allowing it to trap the moisture in the
shop.

This would explain why metal stuff in our detached garage doesn't seem
to rust; it's unheated and quite drafty, so the ventilation must be
helping. The small shed behind it is a different story: bicycles
rust in there, but not in the garage, and I think that's because
there's less ventilation (smaller space, sandwiched between the garage
and a hillock, plus a wood (vs. concrete) floor). Same climate: very
cold winters, moderately humid summers (by Lake Ontario).