Rainwater runs down the glass and into the grooves (track) at the bottom. The weepholes provide a drain for that track. In some windows it's possible that the track will fill up and dribble water down the inside, which should be obvious (the the surface of the inside flange gets wet). The more likely source of water damage to te walls, though, is water leaking behind the window frame at the top and sides. The fix for that is to remove the window (frame & all) and put new sealer (butyl tape of a caulk) between frame and sidewall. There are several YouTube videos demonstrating this procedure - it's not difficult.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC