The material is called "awning rail". It is in plastic or aluminum. With time the plastic will distort.
You put a narrow piece with a "bolt rope" which slides into the awning rail, and then a heavy duty zipper on the other side of this 2" to 3" wide piece.
You will need a heavy duty sewing machine, and special needles for sewing the Sunbrella fabric. There is the option of using the heavier Shelter Rite, which is fabricated with HH 66 glue. This material is similar to what PVC inflatable boats or industrial traps on trucks are made of.
I made the waterproof curtains for the C Dory 25. They are heavier and bulkier than the sewn Sunbrella. the vinyl is heavy duty and clear vinyl glues in well. I used common sense fasteners.