The Plastic Tray is a great option if you are not going to use the functional cardboard box or wooden sleeve. The tray is designed to accommodate the Fresh Patch Large dog grass pee pad (24" x 24").  The grass is easily removed from the cardboard box and inserted in the plastic tray.  The tray is helpful if: 1.  Your dog chews on the cardboard box 2.  Your Fresh Patch is being used outdoors in rain or snow 3.  Your dog needs a lower profile for entrance into the unit