I'm positive on both Covercraft the manufacturer and Carcoverworld the online car cover distributor due to my experiences with both their customer service and product quality.
Our large SUV is used for towing our travel trailer but most of the time it's parked on a pad beside the garage on the southwest side of our house. For 5 and 1/2 years it's worn a custom fit Covercraft Weathershield HD cover exposed to the Tennessee summer heat and UV and winter cold. Over that time, while the elastic has relaxed some, the color and the fabric itself have not faded or weakened. The stitching weathered less gracefully, though, and a seam opened up during a recent windy winter storm.
For a warranty to be worth anything, the company offering it must first of all still exist when a claim occurs and then be willing to honor it and be responsive with their customer service. I was happy to find that after 5 and 1/2 years, the warranty was for 6 years and still in effect both and that the seller and manufacturer were still in business. They responded within a business day to my initial email requesting warranty service. Subsequent communications were responded to in a few hours and very quickly a replacement custom cover was on order. A week after I had provided Covercraft with photos showing the ripped seam and product label, later the new cover arrived at no new cost to me.