Once again I say, I have and do hunt in some of the worst environments for wood stocks (rain, cold, and snow) and again, if you take proper care of your firearms you should experience no problems. If you don't you will experience more problems than simple warping of wood.
Next to safety, the care and maint. of your firearms is the most basic and essential responsibility of owning them. Having a synthetic stock is not an excuse for ignoring that responsibility.