When I had a rear window pane broken by a rock thrown from a vehicle spinning its wheels in my storage lot, I looked through the online listings for "automotive glass replacement" in my area (Sacramento), and found an installer who listed RV's in his list of vehicles serviced. He was able to cut and shape a piece of safety glass to the needed dimensions, and even got it to fit into the frame without removing the frame from the trailer. The storage yard guy (who was spinning his car wheels) paid the bill.