Car covers can help protect your car provided you choose the right one. There are three basic types; water proof, water resistant or "breathable" and non-water resistant. Each has its own advantages and problems. The waterproof car covers will keep the rain off your car, but will also trap condensation between the cover and your car. This trapped moisture may attack your paint with results that are worse than if you just left the car uncovered. The water resistant or "breathable" car cover will repel most of the water yet allow air to circulate, preventing condensation. The non-water resistant car cover material is 100% cotton or cotton/polyester. These are not water resistant and should not be used outside for long periods of time. For indoor use, the 100% cotton flannel cover is the most gentle on the paint and probably the best choice.
Car cover care is simple, and usually involves cleaning it periodically. Read your cover's directions carefully. Most may be washed in the washing machine with a mild detergent and no fabric softener. Dry thoroughly according to the manufacturer's directions. No car cover should be stored wet. If it is removed wet, dry as soon as possible. Solvents, such a gasoline, etc. will usually eat holes in your cover. One more thing, never drape your car cover on hot exhaust pipes as they tend to melt and leave a gooey mess.