David, take the whole foglight housing out, remove the bulb too so it can dry really good inside. Put it infront of a fan for a while. If you seal it with moisture in it it'll defeat the purpose. You'll see where the two parts meet all the way around the housing. Get some epoxy or even silicone and go around the line where the two parts meet, let it dry and you'll be good to go. If it still does it then you'll need to get a new gasket or grommet where the bulb goes in. Then head over to
www.z71tahoe-suburban.com and become a member ;)