I currently use the Arm and Hammer Pet Litter Deodorizer sprinkled in the bag in the drawer (I put it inside the bottom of the bag when inserting a new one) but that ammonia smell does hit strong once it gets about half way full.
I only smell ammonia when opening the drawer or the box is cycling with the hole exposing the drawer, but I'd love to help cut that down more so I'm going to get some of that zeolite stuff to put in with it. I'll try this one for now because the other recommendation above is out of stock.
I got the small odor trap pod and packet from Whisker as they used the technology developed by Fresh Wave (which works GREAT as a product to clean smells from rooms) because I already used Fresh Wave, but I'm not sure that it really works. I didn't particularly notice much of a difference with it, but I might have already solved most of the smell issues beforehand. I have it inside of the drawer.