How to prevent leaks in the cabover area?

I had a problem with leaks in the cabover when my motorhome was new. I took it back to the dealer after our first trip and had it "fixed" under warranty. When it got back I parked it for the winter, and when we took it out for the first trip in spring water was dripping on my wife's head whenever I made a turn. I took it to another repair shop and had the roof completely resealed ( now only 2 years old). At our next trip, water was again dripping into the cab area. I got a ladder and began caulking around the window and lights when I discovered that the marker lights across the front of the cabover were installed upside down. the vent hole which was supposed to be on the bottom of the lights were at the top. As water was running off the roof at the front, it flowed into the vent holes filling the lights and running into the RV wall. I removed the lights and reinstalled them correctly and have had no problems since.