Re: Coscto canopy?
I have that 10x10, and use bricks as well. That said, on really windy days, it doesn't even come out. I'd imagine 30mph winds would wreck havoc, even with some stability at the base of the posts. Those things are pretty flimsy. FWIW, a neat trick I learned....those nerf 'snakes' (or whatever they're called) that kids use as swimming pool toys...if you cut along one edge, they'll wrap around the posts and provide a bit of protection when (not if, when...seriously) the wind kicks up and the darn thing bangs against the car you're detailing.
In terms of size, for anything but really small cars, it makes for awfully tight confines. At that, depending on the angle of the sun (or wind), I still find myself moving the vehicle at least once. I'm not sure if any vendors still make a 12x12, but I used one a truck show once, and it was awesome. Along with the extra width/length, it was also quite a bit taller (maybe 1' or so?), which is really nice.
Cogito Ergo Idiot.
'12 Audi Q5, Phantom Black Pearl; '07 Lexus ES350, Tungsten Metallic.