I found this interesting article here from UC Berkeley about a flow through worm bin design which allows an easy harvesting of worm castings. They call it the "Vermitopia". I am working on building a worm bin like this in my own warehouse to allow for the easier sale of castings. My design is smaller and has a screen on the top instead of a full lid to allow for better air flow, but there are a lot of similarities. I will post pictures of my worm bin in a few days when it's completed, but for now if you want to see a different way to build a worm bin, check out this site!