rear view camera defogger
Those of you who have your rear view TV camera mounted inside a 2.5" tube behind a glass window that fogs up in cold weather can easily install an inexpensive defogger to remedy the situation. I ordered this security camera heater / fan combo from eBay and fixed two annoying problems with one inexpensive purchase:
12V DC Heater Blower Cooler Fan Kit Spare Parts for CCTV Security Camera...
Strap the tiny 12 volt DC electric heater under the bottom of the metal tube the camera is mounted in with a 2.5" metal hose clamp around the outside of the tube, similar to what you'd use around a dryer vent hose. Look in the tiny gap in the wood trim near the top of the tambour cabinet doors with an inspection mirror and you'll see a bunch of wires crammed in there. Carefully pull the wires out and connect the heater to one of the light blue wires. Test the wire to be sure it's really live first. On my coach the dark blue wire is for the bedroom lights, so it only has power when the lights are on. The light blue wires have power all the time in my coach. The white wire is the ground, but you can ground to the same screw the camera uses. Install a switch inline so you can turn the heater off in warm weather. You can leave the heater on all winter because it uses such a small amount of power. It doesn't even get hot enough to burn your finger, but it gets warm enough to defog the camera window after several hours. It's possible to insulate the outside of the tube if the weather ever gets cold enough that the heater can't defog the window.
Those of you who camp in humid areas and have frost on the evaporator of your gas refrigerator can use the little 12 volt DC fan from the above purchase to defrost the evaporator in a few days, no matter how thick the frost is. There's no need to turn off the refrigerator or remove the food. Take the cover off the light bulb inside the refrigerator and you'll see the 12 volt DC connections that go to the light switch. Make two "Y" adapters (a positive and a negative) to run the fan and the light switch at the same time. Connect the adapters in such a way that the fan has power all the time obviously, or else the fan will shut off with the light when the door closes. Make the wires long enough so you can place the fan on the shelf directly below the evaporator blowing air up onto the fins. Turn the refrigerator up one setting warmer than usual. In a few days the evaporator will be completely defrosted and the fan can be removed for a few months until the frost builds up again... So there you have it, two annoying problems solved with one inexpensive purchase! 
Topic: rear view camera defogger