I have no idea what temps fabric does well at. I just figure if it's comfortable for me, it's good for my fabrics. I think if I was looking for storage out in the garage, I would move all my scraps out there before my quilt kits. Since you live in the desert, I don't think you would have too many problems if you put them in containers that could breath. Maybe wrap the fabric in an old sheet and put into cardboard boxes. Mark on your calender when you put them out there and check on them monthly?