I have been breeding rats for quite some time. I never smell them. I house them in racks that are built with water treated wood, and a substrate of Pine Pellets. I clean them every 5-7 days, and NEVER smell them whatsoever. Some people will disagree with this, but I also use Arm&Hammer Kitty Litter Deodorizer, and have been for 3 years now with no ill effects on my colonies or my snakes. You can have 10 rats, the smell that people talk about is honestly, in my honest opinion, is a lack of sufficient upkeep/husbandry. Keep them cool, hydrated, and eating the proper diet, and you wont have any smell.
Trey Jackson
www.tmballpythons.com