I traced out my existing package tray on the smooth side of the pressboard. Cut it out oversized because the original’s edges were curled in. Test fit and trimmed as needed with a cordless jigsaw. When I was happy with the fit I spray painted the whole thing flat black. The rough side is pretty close to the texture of the original.
If your package tray is missing I would suggest you make a cardboard template to your liking and trace off it.