Take the cap off and leave your lights on for a bit, that usually gets the moisture out for me. After that work on sealing them up. Try putting silicone around the cap and see if that works. After that take a look at the seal between the bulb and the headlight itself.
_________________________
1998 Pontiac Grand Prix GT
WizAired CAI, Impala 12" Brake Upgrade, ZZP Alternator Rewire and Voltage Booster, Rotated Dogbone Mounts, Kicker KS690 6x9s, JBL GTO427 4s, JBL P652S 6.5s
2001 Ford F150 XLT SuperCab
Stock, LineX, 212K