I'm on my second one, they have lasted about 5 years in direct sun and I'm closing in on #3.  There are two problems: 1) strong wind can loft the cover.  I use two long bungees to "hug" the barrel but if there were some grommets at the bottom it could be tied down better. 2) Some of the seams leak in years 3-5, particularly at the base of the smokestack.