I blame that on the tires. There's nothing like opening an old sealed kit and finding a tire stuck to the windshield!
Still, beware of packing peanuts. They are good for shipping but I'd be wary of long term storage in the same way you only would use archive quality plastic pages for baseball cards or other collectibles. There's no telling how they will break down over time as they dry out and age. Also, some of them now are water soluble for the environment. I can imagine what humidity could do to these. Mush!