My spare tire cover came in today, it’s an ADCO 1740 (black) for the 12″ wheels I bought for the Trailex trailer. Well, it fits perfectly. Surprisingly so. It’s a “size O” (oh, not zero) found here for under $20 shipped:
I ordereda pair of covers for the wheels for when it’s parked in our hot New Mexico sun and will post back when I know they fit.