I've never had any problems with kits stored long term. I've held onto kits for probably 15yrs with no change in appearance. I've always kept them in a house usually in a dark, dry closet setting.. no major climate changes... A raw boxed wouldn't fare to well in the rafters of the garage though.. I think any exposure to the elements, even heat/cold/UV/etc.. does affect components... if not the balsa, the plans themselves are susceptible to deteriorating over time. Matter of fact my collectors planes(planes I'll never part with, and rarely fly) have been stored for many many years in same controlled environment/conditions with no problems.. and the covering is still in excellent shape. The planes that have seen many hours of UV/heat/cold are the ones that have changed. My 2cents.