heavy-duty zip ties are a cheap way to reinforce the pins holding it together if it feels shaky. also, depending on your climate, having a plastic cover you can remove or peel back during high temps is easier on some plants than one permanently affixed to the frame (plus, as others have mentioned, the plastic will degrade due to exposure over time).
also, i usually place something with some heft (larger potted plants, unopened bags of soil or fertilizer, or bricks, etc.) at the bottom to help stabilize the set-up from wind, pets, and such. have fun!
what idealism does to a mofo