You can replace the window or you can go to a glass shop that specializes in repairing dual pane glass. One such is Suncoast Design Center in Hudson Fl. 727-868-2773. I believe they charge $200/window.
Depending on the window size, you may be able to buy a replacement for $250-$300 and install it yourself. You could check with Fleetwood Parts to see what a replacement will cost.
Former owner of 2004 American Tradition and several other RVs
Home is West Palm Beach, FL