I have a grey 12X20 house-style Cover-IT, and it was great when I was using it (I never got around to putting it back up again after I moved). It is more of a pain to put together than they tell you in their marketing literature, but once it's up, it is a very sturdy structure. I was living at the top of a totally unprotected hill, and when we got storms, the wind blew at 90 mph quite a few times. Although the structure hung in there, it did flex and buffet like crazy - and the flapping noise it made when the air was rushing over it kept me awake at nights. I was parking a Viper GTS in it, and I spent many nights looking out my window with a spotlight just to make sure the thing wasn't shaking itself apart and getting ready to rip my car apart. It always held strong (thank God).
Those screw-in earth augers were great, but they are a nightmare to install. I needed to use a six-foot pry-bar and a sledge hammer to get them to screw in and it took me about five hours to get all six of them all the way in. Next time, I'm going to use those duck-bill things or some industrial tent stakes and drive them in with my jack hammer.
You'll definitely want to make a vapor barrier for the ground, and put some mesh down there to keep the critters from getting in. I put down a layer of 1/4" welded wire mesh, covered that with a heavy-duty Costco tarp, and topped it off with astro-turf. It came out pretty nice.
One other thing you might want to consider are the Handy Home garages. Costco sells them for about $2300, shipping included. I have one, and it's a hundred times better than the Cover-IT, and not much harder to put together if you have a pneumatic nail-gun. Here's a link to the garage:
Link to garage kit.
