is the bottom frame filling with water when it rains - get hose and see - I had a similar area window on my bighorn with the dual pane windows leak upon delivery- first rain the window at top was not fully bonded and water would run ins and down filling up lower sill area faster than the drains that are there couls drain so it was flowing over to the inner wall and down
heartland sent replacement window- if you pushed on top of window lightly you could see gap and where water was leaking in between glass and frame