I bought this fire pit cover to try out as a tire cover and it seems to fit great!
It's silvered on the inside, black on the outside, has a drawstring, and comes with a little zipping storage bag that's about 10 inches square and 1/4 of an inch thick at most when packed. Material is some sort of waterproof nylon cloth.
View attachment 903540
LBTING Fire Pit Cover, 48 inch Cover for 42-48 inch Round Firepit, Waterproof Windproof Dustproof UV-Resistant Heavy Duty Cover for Outdoor Patio Firepit Table - Black
https://a.co/d/inQ6DbA