Best way to store spare mtb tyres/tires?

My big chunky mtb tyres are off the bike for the summer (Brits may insert hollow laughs at my foolishness here :o). I've just left them on top of a box of stuff in the garage, but they're not keeping their shape very well. Does this matter? Is there a way that they should be stored when not on the bike?

Thank you.

Here's an article that talks about storing tires: http://www.tirerack.com/tires/tirete....jsp?techid=37

Are they folding tires or wire bead? If folding they WON'T hold their shape so no worries. But keeping them cool and out of direct light is good, and if hanging them rotating them every once in a while is good practice.

Thank you both! They're not folding tyres, so I'll just rotate them regularly and look for a hook so I can hang them from one of the rafters. They're in the garage so out of sunlight, and it's fairly cool in there too.