I like the idea of the commercial FTWB. I do not like the idea that it must be placed on a concrete slab in order to harvest the castings from the bottom. I created a very easy to build commercial size FTWB that does not require being on concrete to harvest. Instead I us a custom built casting chainsaw.
I raise rabbits and needed a way to easily feed their manure to the worms for final processing. This FTWB has proven to work perfectly for my application. To see pictures and details for building please visit my rabbit web page: http://kferg9804.wix.com/aharabbits and the FTWB at: http://kferg9804.wix.com/aharabbits#!worms/igit7