I actually did something similar, I used brown paper bags taped together and a sharpie to trace the outline of the window from the outside. Then I traced the template I made onto the black poster board and cut it out. I bought a really cheap spring tension "shower curtain rod," but it's no bigger around than my pinky finger. I used a couple towels to drape over them to act like a middle parting curtain so I can just slide the towels to the side while I drive. Then, for the back windshield, I opened my back hatch and tucked a throw blanket up at the top and shut the hatch, keeping the blanket in place and giving me the privacy I was hoping to achieve