I've had issues of 'zinc pest' for some older Intermountain units and Atlas units. I believe the issue was caused by an imprecise mixture of the metal alloys. The temperature and humidity would only make the problem more acute. I have hundreds of Intermountain and Atlas locomotives which I have not run or inspected recently for the zinc pest condition. I might be unpleasantly surprised when I look at them closely. I have not seen any issues with Kato, Athearn, MRC/MP, Bachmann, Lifelike/Walther or BLI models that I have. They are stored in a temperature and humidity controlled environment... but a poor alloy mixture would not keep disaster away. Very likely a particular Chinese factory that made the Intermountain and Altas units was at fault for most of the poorly made chassis.