The holes are good, lets the dirt fall off. I make PCB at home, occasionally. The worst part is drilling dozens of small holes. Very small margin for error. Seeing all your holes, just reminded me of an unpleasant task.
Mine is heavy wall too, only about 8 inches long, thin 1.25 diameter. Just had a bunch laying around, still do... I heated it up, squashed it mostly flat between two pieces of wood. Heated it again, slipped the Fiskars in, squashed down the rest of the way. Drill two holes all the way through for screws. Drilled the topside holes bigger so the screw heads could pass. Holds the knife secure too, doesn't bounce out, or rattle around. Left the bottom open, to let dirt fall out.