Originally Posted by Leodis41
If the camera gear is warm inside and out you will not get condensation forming when you remove it from the top box and case.
A lot of people appear to have this reversed.
A warm camera into a cold environment means it is LESS likely to fog up.
Of course the cold camera placed into the warm case might fog.
If you really need to do something, and I don't think you do, just put a light bulb in there and wire it to the ignition switch. A 35 watt bulb on a big METAL socket (to spread the heat) may do what you want. Anything on a small 9 volt battery will only give you heat for a few minutes.