Taking your lenses out to get fresh air outside is probably not helpful because the outside air is humid. But, I don't think there's much you can do to avoid that when you're out shooting. Just make sure to store them in a dry (low humidity) place at home. Air conditioning usually lowers humidity inside. When you come home from an outdoor shoot, it's probably best to take your gear out of the bag to let it air out in the AC. Any time I get something new (anything) that comes with one of those little desiccant bags I toss it into my camera bag. I don't know if that really makes any difference, but it's easy so I figure it's worth a shot. I've never had any fungus problems.