if you want plastic litter boxes, they are easy to make.
I bought a couple of the sterlite plastic boxes with lids with them. the ones where the top is wider than the bottom.
I glued the lids on. I turned them so the lid (wide) side was on the bottom. I uses a soldering iron and melted the entry
hole on one end of the box. then I poked the hot soldering iron all over the sides for air holes. I did not want the inside of the box to become too hot or humid.
these boxes worked well until the does figured they tasted good, they chewed them to bits.