[Modding the 780T side window to real glass ?]

If a flat replacement window without molded edges could be mounted to the inside of the side panel by securing it with something like 3M mounting tape, I would take out the old window and take it to a glass shop that can make up a tempered glass replacement. Tempered glass has to be cut to size first then heat treated to harden and temper it. Since not all shops can do that, it will not be cheap and you would have to look around to find a shop that can do it (or farm out the tempering step). However, tempered glass is much stronger than regular glass and will be far less likely to break if the side panel should flex a bit. It will also be more scratch resistant and will never discolor with age.