Take a close look at the photos of Malones nice little voltage reference boards (http://www.voltagestandard.com/Home_Page_JO2U.html). The voltage reference chip is mounted on an isolated peninsula of PC board material to help isolate it from stress due to environmental changes. ------------------------ If the humidity effect is strictly from mechanical stress on the die as the plastic encapsulant swells or shrinks, would a part in a metal can then be immune from this effect, even if it was non-hermetic?