Polytunnel - halfway there!

I have just finished building the frame of my 10 x20ft tunnel, corner braces, crop bars and ridge are all on and tight. I'm slightly concerned that the frame still doesn't feel v rigid, it doesn't take much to shake the whole assembly and that's with the posts concreted into the ground! I'm hoping that once the door frames and polythene go on it will feel a good deal stronger. Can anyone advise how rigid their tunnel was at this stage?