Perhaps to make it a bit more wind stable , put a cheapish plastic pea garden net over it and tie 2 litre pop bottles filled with water to the netting with string. So they sit on the floor around the base , adjust the string lengths so there is a tiny bit of tension /weight pulling the green house to the floor .
OR
Still with the net idea, dig a trench around the errected & covered green house save for the door opening . After hanging the net over it, drape the spare net across the trench , refill the trench a bit at the middle on one side only , then tension and refill the same amount on opposite side .
This should allow you to make nice neat envelope corners for back filling over to bring everything nice and taught .
If your soil is so light it will run easily through the netting put a few opened up bin bags on top of the netting in the trench and then do a bit of back filling and tensioning by pulling the free edge of the net .