I have a window AC unit that is ab't a foot short for the width. So, I took two box covers faced them inside to each other so it is quite solid and then placed a plastic bag over each end, now its weather proof--unless the squirrel tries to rip off the plastic to get inside. Worked perfect all summer long. Yesterday, the squirrel leaned up against the box covers and they fell inside and presto! she can come in too! I chased her back outside. Just a little while ago I came home from the grocery store and there she was sitting on my chair looking for the peanuts!