I have 4 trays in a walk-in understairs cupboard in my kitchen. I just use plain and simple open trays, i don't like covered trays, smells build up inside (no matter how clean you keep them) and it is 10 times worse for the cat as their sense of smell is so much better than ours.

There is no smell (well, briefly, if just been used of course lOL!) especially with Cats Best litter.

I also have 1 tray upstairs (for Lacie's en suite facilities LOL!) under a desk in my workroom, and 4 trays out in the garage (which they can access via catflap anytime)