How do I store my gear long-term between seasons?

The golden rule for long-term storage is: never store any gear compressed. 

For sleeping bags, always store them loose in a large storage sack (not the small stuff sack used for travel) as packing down insulation for months at a time can reduce its loft over time. 

Tents and mats should be completely clean and 100% dry before storage (any residual moisture risks mould). 

Avoid storing your tent in a hot, dry shed as sustained heat and dryness can cause nylon fabrics to break down and perish faster over time. A cool, shaded, moderate-humidity spot indoors is a better choice.

Mats should be stored in a cool, dry place out of direct sunlight, ideally loosely packed or hung, rather than tightly rolled, and always with the valve left open.