RustSeal should always be stored in a cool, dry place. Most garages are not climate controlled and subject to cold in the winter and hot in the summer. Because of the range of temperatures and especially the heat in the garage during the summer, it is best not to store RustSeal in a garage. Most people store RustSeal in their basement which typically is a cool, dry place.
In summary, garages are not an ideal place to store RustSeal. A much better option for storing RustSeal is a basement as this meets the requirement for a cool, dry place.
Please be sure you read and follow the complete application directions for RustSeal which can be found here -> https://www.kbs-coatings.com/rustseal-directions
Please reach back out if you have additional questions.