I thought about putting drains in them along with the dams, but decided the size of the pipe needed to allow flow without getting backed up with capillary action was not worth the effort.  So far, the prop wash alone keeps them pretty well emptied.  I have never had more than ¼” of water remain in them after shutdown.  Of course, if I am leaving the plane out in the rain, I put a Tom’s cover over it, as the door itself will leak if the seal is not engaged.  The biggest benefit is the lack of water pouring into the cabin when the door seal is turned off.