If you call Tiara in Elkhart with you VIN they should be able to help. I ordered the bedroom window above the bed for our 39MB, also ordered the gasket to install on the new window.
You just need two people, one inside and one outside, but very easy replacement once you get the molding off and all the screws out.
Be advised shipping is approx the same as the cost of the window, at least it was for me, shipping from Elkhart to the Rochester, NY area.
Michelle & Ann
2018 Chevy 3500HD Crew Cab High Country DRW, D/A, 2016 RW39MB, Dual ACs, Auto Level, Auto Sat Dish, Stack W/D, King Sleep #, 17.5" Sailuns w/Disc, MORryde IS & Pin, Comfort Ride Hitch, 5.5 Onan, Res Fridge & Induction Cook Top