Even if bows produced any heat for the wool to trap i don't see it being a problem, even in the summer. I live in utah so its pretty dry and doubt the humidity would be great enough to cause problems. Trapping moisture against the sinew is my only concern with a cloth covering. As long as i don't use it in the rain i won't have problems but in the future i plan on gluing and finishing it in a water resitant way, like a mod podge.