You will want to remove the entire window FRAME from the trailer.
Trying to remove the glass from the frame most likely will result in the window glass shattering into a billion pieces. That glass is "tempered" which some folks call it "safety glass".
PLEASE NOTE: This IS NOT THE SAME AS windshield glass, Windshield glass which is not only tempered but laminated with a layer of plastic sandwiched between two pieces of glass.
Breaking tempered glass will cost you more to have it replaced if you break it..
Once the frame has been removed you can figure out your own homemade replacement frame (wood, vinyl or aluminum, your choice).
Save the old window and frame in a safe place (where it won't get broken or damaged) so when you want to sell or trade the RV you can put it back in.
