Here in northern Iowa we get brutal cold in the winter and 80%+ humidity in the summer. If you cover with film you will notice all your models covering will need to be re-shrunk from time to time. Usually in the spring after the winter is over. I think that is a function of the wood drying out a bit in the drier air of the winter time. Other that, as long as the wood stays dry, as in no standing moisture, you should be OK.

Ken