Jerry,
I've not found any drain holes on the roof for my AC units, the moisture just collects on the roof and eventually drains off the front or sides (depending on how level the coach is).
I've found if you keep the condenser and evaporator coils clean that helps prevent the dripping inside the coach. Also, there are some opening in the base of the AC unit that you need to ensure are clear of debris so water will drain out of the unit. My front AC unit was leaking earlier this year and I cleaned them both real good and have not had any problems since.
Watch out for wasp nest when you remove the cover, that's no place to be swatting at wasp. Voice of experience.