Skyflame Universal Stainless Steel Pizza Oven Kit with Stone for Most Gas Grills and Pellet Grill Conversion Kit, 22x15 Inches

Even better, they make Stainless steel "covers" that go a few inches over the stone to hold the heat. This lets the stone and the oven (under the cover) get a lot hotter. They turn a gas grill into a real pizza oven. https://www.amazon.com/Skyflame-Universal-Stainless-Grills-Pellet/dp/B078LSSZ13or get an all in one option like this: https://www.amazon.com/Masterbuilt%C2%AE-Accessory-Porcelain-Coated-Stainless-MB20181722