I had the same in mine, turned out I needed to secure them much more tightly in the car.  I was securing them finger tight and they need to be tightened with tools which pulls the entire light together and creates the water tight seal.
I took mine off the car and used a hair dryer to get rid of the condensation.  Been fine ever since.  If you have a lot of water, drill a tiny hole in lower corner towards the wheel arch side of the light.  Underneath of course, this will let the water out and it wont get back in from underneath.