BLB: correct, that's how air can contain moisture at normal temperatures. Even below freezing water has a vapor pressure, which allows ice to sublimate (see what happens to ice cubes that are kept long in the freezer).
Have fans ever been used in hybrids? Pressure shouldn't affect one much, though temperature could be a problem with high mixes. I was planning to include one and have a wiring for it, but I don't have one small enough.
A metallic fan could work even if a computer fn would melt.