You have two choices really: either seal the units so that no water can get in... or allow the free movement of air in and out. The best way I found was leaving the covers off the lights and going for a drive. The engine heat and circulating air dried them out a treat. I have heard of people using vaseline on the seals to keep the water out! Now I have HIDs, the extra heat seems to dry them a bit too! Best way is to drill some holes in the back cover probably... Good luck!