I don't know what it is called, but I had to replace the sash on the tailgate of my old full size jimmy. The glass place I went to for advice sold
me for just a few bucks, a strip of rubber that goes between the glass and metal. You tape it to the glass, rub it with oil and quickly slip the metal sash over it, the swelling rubber then holds everything in place.
The RV service center may even be able to help you out with that.