I would think that the only thing you might want to be careful to do if you have your kindle in a baggie in a cold or hot environment is to make sure you let it come back to room temperature before you take it out of the plastic. I used to keep film in the freezer in plastic bags, and carry my camera out in rainy or cold weather in a plastic bag. You just don't want the condensation to form on anything INSIDE the bag, and if you let everything equalize, it won't. My experience, anyway.
