I have about double that number of rats in the same type of mason pan racks but mine are in a barn with good ventilation. 400 rats in a closed room are going to smell. I have a couple of suggestions which may help.
Good exhaust ventilation - you will need more than a small bathroom fan. You will most likely need an a sizeable intake as well as an exhaust fan. A small exhaust fan pulling from a closed room probably isn't effectively moving alot of air.
Garden Lime - try buying some garden lime available at home depot, Lowes, or any large garden center. Sprinkle a cup or two in each tub with your bedding. The lime will help neutralize the nitrogen in the urine and help knock down the ammonia smell. Not much you can do about the other order other than increase the frequency of bedding changes.
Good Luck with the critters.
Grant