if you're sure everything is sealed and theres still a little condensation to get out, go to the hardware store or Walgreens, Home Depot etc. and get Damp Rid
http://i22.photobucket.com/albums/b345/jahselectah/105684_front200.jpg
with a paper towel, make a little packet with this stuff inside(use masking tape). open your lamp from the circle in back as if changing a bulb, and insert the packet. if you are planning on driving soon place it as far away from the bulbs as possible. (paper towel may catch fire) best to leave this in over night while the car isn't gonna be used.
do this every night with a new packet until theres no more condensation problems.
when you remove the old packet, it should be damp. if it is not then you have no more condensation