We recently adopted a second cat and needed a way to keep her from hiding in the nooks and crannies of our garage where the litter box was situated. The main concern with the litter box in the garage was having a frightened new cat escape when the main roll-up door was opened.
I already had a kitty portal cut through the door to the garage so the next step was to see if there were any storage boxes that would fit the bill Home Depot had a translucent storage bin that works great.
Step 1: Mount the Box
It was easy to mount the box on the back of the door with two screws and cut a hole to match the kitty port. The top comes off to clean the box.
Step 2: Box Is Ready for Business
The top is flexible enough to fit on the box and the handles lock it in place so the cat can't get out. It is transparent enough that the kitty can see into the garage and so far she seems happy. It also keeps the litter out of the garage. So this was a nice simple twelve-dollar solution to keeping the new cat confined. The only caveat is that the size of the box limits how wide we can open the door to get into the garage. That's a compromise we can live with to keep our precious pets purring.