Do not store decoys in the garage attic/ceiling where there is high heat--SC mentioned the results. Best to have them stored on the garage floor, basement, or a well ventilated storage shed works too that is out of the hot sun.
As for full bodies like BigFoots, do not stack them more than 3 high as their weight, with the warm weather will make dimples on the body to the decoys at the bottom of the pile. These dimples may not readily pop out beeing it was dimpled all summer long. So keep it in mind so you will have many years of trouble free decoy use.