A few years back I was working in Phoenix, and to protect us from the desert sun we had what I would call an ez-up on steroids. It was framed in galvanized steel, and staked into the ground. In the summer heat you can get some intense thermals. These dust devils are stronger then I ever imagined. One day we were out earning our money and from about 1/4 mile to our west you could see one of these dust devils making its way toward us. When it was obvious it had our destination in its sights we cleared our equipment and backed away. This particular one was about thirty yards wide. That thing hit our tent, ripped the stakes out of the ground, and to our amazement took a ride that was about thirty feet up and traveled about a hundred yards or so down range. Sadly the galvanized frame did not survive.
The moral of that story: If you cannot adequately anchor or minimize the sail effect of your cover, quickly, you and your stuff are at risk.
Gary