Scott,
When I lived in Wilmington, NC. my workshop was located over our garage. I 'over' insulated the room and with a 10,000 BTU air conditioner kept the room quite tolerable during even the worst heat. I really agree that exposing our models and modeling supplies to prolonged high heat is not beneficial to their longevity and you'll enjoy spending time in your shop a LOT more in comfortable temperatures (and humidity - another benefit of A/C). I don't mind sweating at the flying field, but I hate dripping on plans and fresh balsa .
-Will B.