That's sort of a double-edged sword. If you take good care of your gear, make sure everything is completely clean and COMPLETELY dry, then there shouldn't be a problem. However, many people put away their gear still wet, or even damp, thinking it is dry. In this situation, you're basically setting up a mildew and bacteria farm by sealing it in a dark, poorly ventilated container. The other side of this coin is where you actually store it. If you get some sort of container that is not airtight and store it in a basement, a garage, etc., it could get damp/moist, and there you go again.Both of these situations will only really affect your booties. The fins, mask, and snorkel aren't nearly as susceptible to the heat and moisture, but rubber and plastic can melt. I have also heard some horror stories about using gear that has been improperly stored for some time. Long story short, as long as everything is properly taken care of, your mask, snorkel, fins and booties should be fine.