If you have a lot of condensation, try using a paper towel and rice. Wrap the rice like a burrito full of rice. Tape the paper towel shut and stick it your housing overnight. If you modded caps to fit HID's or something similar, you may want to use a cap that is still sealed, so the rice will absorb the moisture in the housing and not out of the air. It's not completely necessary to use a sealed cap, just more efficient. Worked very well for me, as I acquired a lot of moisture from adding a modified end cap and going through the car wash before properly sealing it.
Credit for the idea goes to Mike1220.
-Skeet