The problem with that is going to be the frame for the window I believe. When they build the slide most modern motor homes build walls out of aluminum tubing. This wall has openings framed into it out of aluminum tubing to support the frame. Then the frame is covered in Styrofoam and then the inner and outer wall are glued to the frame in a vacuum sealer process. I am not sure how you would be able to put the frame in for the window.
Maybe someone else that has done it can help you if it can be done