I guess it depends on the environment. In Virginia, it gets really hot and humid in the summer and cold as crap in the winter. This causes yellowing, warping, mildew, and plenty of other bad stuff for toys or comics. So I've always kept my collection indoors where the environment is controlled and air-conditioned. But hey... whatever works for ya, you know?
Aren't you concerned about your collection being out in the garage? Nothing does more damage to a collection (besides smoke) than the variable temperatures and humidity inherent in a garage environment. Regardless, that's a very impressive collection!