The silicone strips are shower door seals that you can find online. It came in a 10 foot strip for about $12 that you can cut to size. The one I got was for 3/8 inch thick glass which just happens to be the thickness of the lid. Unfortunately the IM lids are a little thicker at the corners hence my cutouts at the corners. This way the stripping lays completely flat on top. Without the cutouts, there would be little wrinkles because the stripping is not thick enough at the corners.
Great idea. I lost my favorite fish named Yazz, a Yasha haze goby, from somehow jumping out that little crack opening of my IM SR-80. He lived with a tiger shrimp and surprisingly, a yellow watchman goby. I was so upset. Also find snails going for walks outside the tank.