Fat Cat, the one I bought is a "Premier Semi Custom Car Cover." It's in a box with a picture of one of the covers being pulled over a new Mustang. Its "size" is K-3 and it cost just about $42.

Unlike the pictures of the custom ones I've seen, it does not have pockets for the side mirrors to slip into, which means it's kind of tight on the car. I think the recommended "size" actually refers to the original Challengers, not the modern ones. However, it seems to work well enough. I use it outside and it hasn't blown away (yet, at least) or anything.