Please no WD-40 in the track you'll end up with a black gooey mess. There is a new- no tear- screen fabric which you can get at Tru Valu, Ace or any other good hardware store. It is light enough to fit easily into the smaller track and will not tear. This fabric is great on screen doors since it will take abuse from many small hand and even big fingers. Your local Tru Valu will cut exactly the amount you need and unlike the big box retailer you will not have to buy a 1000' roll.
1994 30' Excella 1000, Chummy III- Ford Excursion- 7.3 Turbo-diesel