I have had spray basting hold indefinitely -- several years, actually. :oops: That was on a baby quilt, but I would imagine it would be similar for a large quilt.
Storing a lot of basted quilts might require some thought. I would think rolling them would be easiest. Maybe set up a hanging device in the garage with large pvc tubes and roll the basted quilts on the tubes.
I would probably machine baste or pin the edges of a large quilt just to make sure the edges don't start separating from handling.