Car Covers - What's best?

I just bought a cover from Griot's Garage and it fits my 65 Fastback beautifully.

If it parks outside, most covers will deteriorate in the elements.

I store my 67 coupe in an outside space in a storage yard when not in use. I have a cheap generic cover, then thick pieces of foam about four inches thick and a white plastic tarp over everything. The foam gives an air space so when it rains, the plastic tarp won't stick to the other cover. Plastic tarps will stain your paint when it gets wet. I replace the plastic tarp about once a year due to the sun eating it up.

You could shrink wrap it like is commonly done with boats and RVs