Hey Doug...
Just my 2 cents, my boat has Dacron sails, so I remove them, clean and complete any repairs to them, thoroughly dry them then store them in a heated area (mine are in my basement). The previous owner of my boat usually rolled his main around the boom and it picked up several rust / mold stains and some tearing along the lower part of the sail.
If I had to store them as you described, I would make absolutely sure that the sails were 100% dry, that they would not be exposed to too much humidity when stored (yes, there is humidity even in the middle of winter), that no metal parts were in contact with the sail cloth, and they were covered in a water-repellant but breathable cloth.
If your sails are mylar or some other fabric, then I don't even have 2 cents to give you!
My boat has its original 27 year old sails and they are in surprizingly good shape--it used to be sailed on a lake.
Good luck!
Mark Owens
1976 H16 sail # 19857