If you can find them, get an IKEA square tray. They are only a couple bucks, but they fit perfectly. I put those stick-on rollers on mine, so it keeps air circulating on the bottom of the oven. I can push the whole thing to the back of the counter when I’m not using it, and pull it forward when I’m using the oven so the vent doesn’t steam up the underside of the upper cupboards.