I just bought a cover from Covercraft. They have several different fabrics available, some for outdoor use and some for indoor. One thing to be aware of: on their website they talk about 'custom fit' covers. However this really only applies to late model cars. For our GTO's what they have are some generic fit ones that actually do fit well, except for one thing: even the outdoor covers do not have sleeves for the radio antenna. They expect you to cut a hole in the cover and install a supplied plastic grommet to fit over the antenna. This shouldn't be much of a problem for an indoor cover but if you care about 100% weather protection on an outdoor cover, it won't be.
However with all that, I did get into a chat "discussion" with one of their reps online through their web site, and after ummm "expressing" my concern about that little detail and saying that I thought it was somewhat misleading, he promised that if I bought one of their outdoor covers, had it shipped here, then marked it myself for the proper location, I could send it back to them and they'd add an antenna sleeve at no charge. He said that was "a special deal" that they occasionally offer to customers who are concerned about that. FWIW.