The Abba patio outdoor/porch 3 triple seater hammock canopy swing cover, the Classic Accessories 55-170-015101-EC ravenna canopy swing cover and the Bosmere C505 swing seat waterproof outdoor cover are good outdoor canopy swing covers. Each of these canopy swing covers has a 3.9-star rating or higher on Amazon.com, as of January 2016.
The Abba patio outdoor/porch 3 triple seater hammock canopy swing cover has a 3.9-star rating and is for indoor and outdoor protection. It covers swings that are 80 inches long by 57 inches wide by 72 inches tall, and it has an adjustable hem cord to fasten for windy days. It is also fire resistant, mold and mildew resistant and machine washable.
The Classic Accessories 55-170-015101-EC ravenna canopy swing cover fits swings that are 78 inches long by 60 inches deep by 72 inches high. It has UV-stabilized coating and a waterproof laminated undercoating, four buckles to keep the cover secure in all weather, elastic hem cords and structured vents to stop wind lofting and mildew. It has a 4.4-star rating.
The Bosmere C505 swing seat waterproof outdoor cover has a 4.6-star rating and is made of PVC-backed waterproof polyester. It protects from wind, rain and the sun, has brass coated eyelets and heavy-duty ties with security cord locks and covers a swing that is 80 inches long by 49 inches wide by 67 inches high.