I'm getting ready to cut a block of minicell foam into bulkheads. I checked out the bulkheads in my Sealution to see how they were put in and noticed a groove cut along the perimeter. It's about 1/2" from the edge, about 1/2" wide and maybe 3/8" deep all the way around on both sides. I'm sure it's there for a reason but I can't figure it out. Does anyone know?