Fill that up with small pine flakes and it will be easy to keep clean. Put a board on the front so the litter stays in place and you can scoop out poop as needed.
@WitchyCatlady There's a ledge along the front, as well as all sides. I will fill with sand and PDZ rather than flakes. Farm & Fleet apparently stopped selling PDZ and couldn't order it, so I'm going to drive the 20 miles to Tractor Supply, who does carry it.