No, but seriously.... Licking is the way to go... Anyone ever tried Rain X. That stuff is awesome for wind shields, so it might be worth trying some of that. I once had a wagon, and the wipers didn't work. I just used Rain X, and got by without windshield wipers for like 6 months.
Okay spit and lick is not for fog, spit and lick is so you don't get water droplets on the dome/lens port. For fog you only 2 choices leave camera in cool place or leave the camera in a warm place. You need to try and match the temp of the water, so normally if your shooting during the summer try not to have housing in the car for a while before you got to shoot. You shouldn't really have any probs. during the winter. But if your stuff keeps fogging up as soon as you got out put it under water and just keep holding it there until the temps even out. Normally if you upgrade to a higher end camera/housing you don't have this problem but those are the only things you can really do to help stop this.
Start by loading the camera into the housing in the driest climate possible, (this week has not been a good time for that I know) like in an air conditioned room, or a space with low relative humidity to eliminate the moisture in the first place. Then, take a fresh dessicant packet (like they pack new cameras and lenses with) and include that in the housing before sealing it up. They also make an "Anti-Fog" application or wipe for interior car windshields, so that might be worth a try.
The key is eliminating as much relative humidity from the interior of the housing BEFORE you seal it up. Inside your car, that happens to be full of wet wetsuits and boardbags, while sitting oceanfront at your favorite spot is not especially conducive to low humidity even if you have the heat on full blast. Good luck, and be sure to let us all know what really works best. Spit is for skin diver goggles and it's surely got plenty of its own toxins, even if it is your own saliva. . . AND it has 100% humidity.
If you haven't experienced it yet, taking a lens out of your cold car in winter and walking into a humid sweat-filled basketball game or wrestling match is a sure fire way to generate lots of fog on your lens, and in a worse case scenario, even the inner elements fog up on you and you're dead on the floor until the lens warms up and acclimates to the environment. Metal mounted optics are especially vulnerable to fogging.