I read alot about putting cold air into the gopro prior to setting out. there is one problem with that, cold air holds moisture. The more you run the camera the more it heats up thus heating the cold air. where is the moisture to go?? to the furthest away from the heat sorce being the battery thus fogging up your screen.
If you put the camera together in a warm enviroment you will have no probs. Myself and brothers swear by the gopros they go in paragliders, RC planes, Surfboards, SUP's, Kite's and dive to have no fogging up of screens, we have gopro and gopro2 and have had no issues. Water temp is around 19deg with morning paddle temp down to 5 degs..
Maybe before you assemble gopro befere a big paddle or the like, have it sitting in case whist on charge as the the camera case is the same temperature as the gopro thus elimaniating the difference in temperature. I dont use the antifog inserts, just aware of climate when putting gopro together.
Thought i better put my couple of words in.
Happy Recording!!!