I’ve used the Hamilton Classics covers outside. They generally work well. Totally waterproof and breathable to start with but start being less waterproof after a year or so. Quality of the straps is not always great and the seams start to tear on the bumpers after a few years. I use one on my Traction now which is about 8 years old. Held down by bungees. Still waterproof enough to allow me to keep the windows open. Fleece inside may damage the paint – it made the clear lacquer coat on my Chrysler go dull but hasn’t affected my Traction paint. That may not happen in a garage.
Chris