Vince,
I've never had much luck with car covers on my 59 because the cars are so big compared to cars made today. The points on the rear fins are murder on most car covers. While I don't have a suggestion for the cover, I do have another suggestion that you may find helpful.
Find a good sized thick cardboard box and cut out the corners, including about a foot of cardboard all the way around, then cover the points on the fins with the cardboard before putting the car cover on. The cardboard will protect the car cover from ripping to shreds on those points.
Good luck!
Michael