Sports gear is stored wet far more often than it is stored badly in any other way.
What actually destroys it
Damp, because gear is usually put away after being used. Mould on fabric, rust on metal, and the smell that will cost you a sale later.
Tension, in strings and anything sprung, which relaxes and sets over months.
Heat, which ages rubber, foam and adhesives.
Compression, which flattens padding and grips.
What to do instead
- Completely dry before storing — longer than you think, at every seam
- Clean, because what is left on gear is what grows on it
- Hung or standing rather than compressed for anything padded
- Out of the sun, away from an outside wall, off the floor
- Not sealed in a kit bag for months
By item
Bats — stable humidity, upright, not leaning in one position for years, and not in a very dry air-conditioned room for long periods. Rackets — in a cover, flat or hanging, away from heat. Strings lose tension whatever you do. Shoes — aired, stuffed lightly, never sealed in plastic. Weights and metal — dry, off a damp floor, which is where rust starts.
What it costs
Nothing except the hour between the match and putting it away.
Questions people ask
Should I loosen racket strings for storage?
They relax on their own. The useful thing is to record when it was last strung.
Do grips need replacing after storage?
Often, and a fresh grip is a selling point if you say so.
Is a balcony acceptable?
No. Sun and rain are both there.