Now I use those http://www.homedepot.com/p/Plasgad-M...101A/202086173, built the rack from scratch to the specifications I needed.

In the past I used jumbo cat litter pans for which I made a DIY http://stewartreptiles.com/Articles/...eding_Rack.pdf , the litter pans are now triple the price of what they used to be so using concrete mixing tubs is cheaper and the rats also have more room.