Never used tire covers myself. I don't see the logic of using them, especially when they should be replaced, regardless of mileage, every 5 years or so. My first set of tires (worn out at 30K miles or so) saw lots of desert sun, and I saw no cracks in the sidewalls. However they were only about 3 years old when I replaced them.
First time I saw covers on rv tires, I thought they were there to keep dog pee off of them. Seriously.
2011 Dodge Ram 1500 HEMI Quad Cab
2011 Jay Flight 26BH