I made some for my overflows out of black opaque 1/8" acrylic. Work at a cabinet shop, so it helps. I did it to block light to the overflow box, was getting a lot of algea I couldn't get to, and to stop snails and such from ending up in my plumbing, causing a jam. Was really easy. Template your shape , cut it with a hacksaw, and sand it smooth. I actually had to make my overflow boxes out of the same material. I bought a Marineland 180 that was stripped off CL
, no filtration at all. But what a steal!! Good luck!