Concrete block outdoor worm bins

[cowabunga61]

I would like to know if anyone has or might have seen in either books or internet an outdoor worm bin design constructed of concrete block with a metal tray in the bottom that would slide out to permit worm castings harvest. I am going to build worm bins under my rabbit hutches to harvest worm casting for my wifes greenhouse. I am only planning to raise a few rabbits (maybe 5 or 6 litters per year) and am not interested in selling worms for profit. I am only interested in castings and/or "worm tea" for my garden and green house. Any help with information will certainly be appreciated. I have been searching the internet for companies that are raising rabbits/worms and have had no success. Thanks for any help. T.C.