Not sure how well this would work for your application, but I keep one of these Bone Dry Dehumidifiers in my car all the time. Its meant to be used in something like a gun safe, but I use it because I live in the Seattle area with an apparently not watertight car. I was tired of having windows that would take forever to defog on the interior during the spring/fall/winter. Works great for my application, I might have some fogging when I first get in and start the car, but nothing like before. Recharge it every 2-3 weeks or so, takes a few hours plugged in then it's good to go.