To insure a perfect fit between the lid and box, I applied a layer of epoxy, thickened with 407 filler, around the top of the box. I placed a sheet of plastic over the epoxy, then set the lid in place over the box. A couple of weights placed on the lid helped the epoxy conform to the exact contour of the lid. When the epoxy cured and the plastic was removed, I had a perfect lid-to-box fit. Note the drain pipe at the bottom of the box.