the baking powder is to reduce smell right? have you considered changing the type of litter you use. i find that yestersdays news (brand name, not just the newspaper from last day) is the best at odor control. you can get 30lbs of it for about $12 before taxes now too. i've been able to find it in the pet section of food markets now too, as well as department stores such as walmart, so you don't have to make a special trip to the pet store whenever you run out either. shredded pieces of paper towel and newspaper, while fun for the rats to play in, does nothing for odor control. you may also want to consider litter training them if you have a large cage and need to fill it with a lot of litter.