Pull couple screws at each corner at top of window. If one side is lots more rusty than other side you could have a leak coming in from above. The water you see is flowing down to the weep hole drains from above. Easy to check out.
2003 Majestic 23P... Northwest travel machine
2013 Arctic Fox 25W... Wife "doll house" for longer snowbird trips
2001 "The Mighty Dodge"... tow vehicle for "doll house"