I just ordered a bunch of stuff from Rich at Reptilebasics. He has the BEST customer service I have ever dealt with. As far as spacing I cut 4 2x4's to the height I wanted and placed them in the corners and screwed my shelves on.I want to say I left about a 1/8th gap all around the tubs. I am getting ready to build a rack system that will hold 30 41qt tubs. I will get some pics up when I get it built.