OK, so I am building a combination rat and mouse rack. I *was* planning on making it two units wide, 4 levels - bottom 3 levels were gonna be jumbo kitty litter pans, top level was gonna be large kitty litter pans. I was impressed by Cas' rack and was hoping to do something like that. Now when I went to get them I learned that the edges on them are bowed, the larger the pan, the more the sides bow outward. Here's my question, how would I keep the pans on a track if they don't have straight edges??? Thank you for any help