I had a question about your spacing between tubs and top of 2x3? I went with 8 inches off the bottom of one rack to the top of the other which gave me around 2 inches between tub and top of rack under it. Seems more than enough air movement and still gives lots of room for food. I would have to agree with you on the 2 x 3's though, they give more room for food and definatley give more stability. I wanted a mixed rack for ASF's and Rats so I did bottom 3 with 1/4 inch mesh and top 4 with 1/2 mesh. I also had some left over 2 x 2 so I put 2 x 3 racks on top and bottom and shoved a feew 2 x 2 racks in between. So far it only saves about 30-40 cents per 8 ft of board and for me no space issue as I made mine 7 tubs high anyway with the 7th tub right at about 68-70 inches.
Just wanted to thank you again Tom for all your insight into breeding rats.