Yes, I replaced a window in my Flagstaff 21 FBRS. It was really very easy. The one over the sink was a crank out type that let in very little air. So I ordered a slider type and it took only about an hour to interchange them.
I got the new window from Pellandent
https://www.pellandent.com/ They were very helpful in the ordering process. Only two gotchas in the work. I had to remove the old window before ordering so I had the wall thickness right and knew the radius of the corner curve. Then I could order and wait for delivery. The delivery cost was almost as much as the window. That hurt.
Good luck with that.