In regards to the ventilation, I was going to just drill several holes consecutively to make a vent similar to what you achieved and then sand the edges down for a more even look. Seems like it should be pretty easy to achieve. If I try it out I will let you know what happens.
I've tried drilling overlapping holes in a bucket with a paddle bit without much success. When I tried it I ended up tearing the plastic around some of the holes. Please let me know if you find a technique that works.
GW, try it with a hole saw instead of a paddle bit. Make sure the center pilot drill is sticking out far enough. Try spinning the drill slower, sometimes fast isn't the best. You might have to speed it up if the hole saw gets hung up on the plastic.
