I have a 2017 Melbourne L and have a screen that I fabricated. PatS above has got the plan, buy a kit at your local hardware store, cut to size according to directions. I cut it so that it actually fits into the existing tracks. I then cut some reflected to fill the gaps and further secure it into the frame. To hold the window out, I used some wood dowel (left over mop handes, and notched them to hold out the window. This was no problem for me as I used to own a glass shop where, among other things, we fabricated screens. If this seems a bit daunting to you, I suggest finding a friend who is handy with this kind of thing.