I had problems with my mini greenhouse blowing over too. Walking around my neighborhood I came across someone with a unique way to solve this problem. They placed their greenhouse right up against an arborvitae hedge and strapped it all the way around the trees.
Now my little greenhouse is reduced to the bottom two shelves and no covering. I use the shelves for my potted succulents (outside). It is a little wobbly but then again it is about 15 years old now.
