Blues Cruiser,
I looked into this several months ago and found out what Mike stated is true. I had my local canvas maker do the job for me.
To aid the project, I removed one screw at a time from the window frames (two at the upper left and right and one at the left and right at the bottom of the frame. I replaced the factory stainless steel screw with a snap that has the same screw size on the back. I coated each snap/screw with TefGel, before screwing them in, to aid in elimination of possible electrolysis.
My canvas maker made a very nice cover for windows using the same model Sunbrella, that is everywhere else on the boat. She also made a cover for the back of the boat and a cover for the gas tanks. The cover for the back is the Sunbrella and the cover for the fuel tanks is synthetic mesh material, typically used to cover outside cushions on yachts. The mesh is the cream color of the deck trim, while the Sunbrella is green, to match the major trim color of the boat.
I will take and post photos...