I've been storing planes in an unheated/uncooled garage for over 20 years with no noticeable problems with the airframes.  The Texas heat here is often over 100F during the summers.  I've not seen any warping of wood frames, but it may be due to the extreme aridity of our area.  I can't tell that the balsa is any drier or more brittle than that on any other plane of comparable age.  No covering problems, and still have a couple of 18-20 year-old planes with their original covering that are still flying.  Over the last couple of years, I've had to re-hinge a few pinned hinges that were put in with epoxy on the older birds (12+ years) due to the epoxy releasing from the hinge material.  Don't know if that's heat/cold cycling or just age.  The shop is heated and cooled, but just not enough space for all the toys!

Bob</p>