Good outdoor car covers are expensive. Talk to fellow car folks who are using them and search the internet. The major problem is moisture evaporating from the ground up into the underside of your car, even when it's covered. Then the rusting begins. If affordable, find out the cost of inside storage spaces in your area. Start here:
https://www.google.com/search?q=king...hrome&ie=UTF-8
Do any of your neighbors have an empty garage you could use?