Damp is the main enemy as alluded to above, fungus will form if damp prevails. My lenses are stored in a room with a solid fuel stove in winter, which promotes a dry atmosphere. In addition, all my bags have silica gel sachets in them at all times. When you come into the warm after an outside cold/damp shoot, unpack your lenses and camera and allow them to slowly come to room temperature before storing as above.