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I first measured my windows and made a frame out of 1"x2" furring strips. The "boards are scrap 1/4" plywood left over from building the coffin. I arranged the boards around the frame until I thought it looked good. I then screwed all the boards down to the frame
I used some black landscape fabric to cover the back of the frame.
To attach the 'boarded window' to the real window, I used two hooks screwed into the window frame and two eyelets screwed into the 1x2 frame. The 1x2 framework is easily hung and then removed.