iDesign Plastic Under Sink Mat Tray for Kitchen Cabinet, Bathroom, Entryways, Office, Mudroom, College Dorm, (Set of 2), 17" X 13" X 2", Black

My bun was <2lbs at end of life so I used https://www.amazon.com/dp/B075FL9DW2 Had a puppy pad on it and put hay directly on one side of the tray. I'm sure I could have placed hay box next to the tray but my bun was tiny and I needed to monitor intake closely.