I plan to put a tension curtain rod in the Habitat then sew a fine mesh screen with velcro on either side. My habitat has the carpet interior I will velcro the sides. I plan to have magnets in the center of the door for closure. I don't have my Habitat yet but I might velcro the the top as well depends on how well the velcro sticks. You could use snaps on the sides if you don't have the fabric. I have a bed rug on my floor so velcro will work on the bottom, a weighted hem, or magnets. I don't think this will be a difficult project. I will likely treat the screen with the pyrethrin they have for treating clothes. The opening above could likely be fabricated from a camping tent. You could cut out the screen door panel and cut and sew to fit the opening. A friend re-purposed a tent he pick up at a yard sale, made a dandy privy tent, and it cost something like $20.