Harbor Freight sells either 10x20 "carports" or now a 10x17. This latter I think comes will "full sides."
These work well. I used one over my chicken pen and it lasted a couple of years. My experience is that the Harbor Freight cover is not quite as nice or strong as the Shelter Logic version of the same thing. But a couple of years for (then) about $100 on sale isn't too bad.
You want to get the plastic "screw anchors" to fasten down the corners against wind. Problems come usually with wind and invariably you'll bend "tube No. 2" which is actually the largest quantity of straight tubes. New tubes are available on Ebay.
I might get the car "shrink wrapped" like a boat against weather and THEN put it under the Harbor Freight topper.
Around here "shrink wrapping" goes for about $13 a foot. For a 15 foot car perhaps $200?
Joe K