My tips for fog free, Use the anti fog inserts ($5 on eBay for 20) but if you're too tight to buy them just fold up a square of paper towel and put it inside the back door. Seal it up the night before and only open the case if you need to swap batteries, make sure your hands are dry before doing so as the slightest bit of moisture in the case will cause fogging. Once you've changed the battery give the case a blast with the cars air con and then pop in the camera and quickly seal the case. Lastly buy the dive housing and you'll be fog free forever, even if the dive housing does fog it just happens around the outer edge of square glass and doesn't effect the lens unlike the dome of the standard housing.