I forgot to mention that the bulb seal could be bad, take the headlight bulb out and make sure that it has a complete seal all the way around the rubber gasket ( some models use foam) if it looks suspect, you can leave all the bulbs out and park with the headlight so that it will get sun for most of the day, occasionally blow fresh air (you can use a computer duster can) into the housing to displace the moisture and you won't have to drill or disassemble anything. put everything back together and see if it happens again, then it might be the housing to lens seal.
2014 Fleetwood Discovery 40G -> 06 Rubicon LJ
Mechanical and Electrical Engineer
Team 065 and 0232 "De Opresso Liber"