I'm having the same issue. I have only three girls in a two-level ferret nation cage. I use fleece bedding.
I scrub the cage really well each time I clean it, and often do a double-wash on the fleece. I do leave them a few "rattie scented" things: their house ball on the first level and their hut on the second. These things are pretty enclosed and don't stink from the outside of the cage.
The cage lasts only two days before you can smell it all throughout our living room. My husband is particularly sensitive of smell, and notices it quite strongly.
I would love to be able to clean the cage every three or four days, but right now I have to do a complete cleaning every other day or it gets noticeable.
