When I was waiting for my metal tray to come in I made a fleece pocket for the plastic tray. I sewed 3 sides and then slid the tray in and had enough fleece on the open side to fold it right under the tray.
It was a pain to change it but it was only for a few days while my tray came in. There was no way for my chin to get at the try unless she ate through the fleece but luckily she's not a fleece chewer.