I have considered braces utilizing threaded rod and turnbuckles. I wouldn't think you would need very large rod because of the strength of the steel. You could use the turnbuckles to provide the exact amount of pull or push on the opposing panels. With the small amount of raw materials used you shouldn't have to adjust much for the displacement. The only thing that I think to consider and have discussed lightly with Wayne is resonance of the steel. I think we decided it to be a non issue. Just more food for thought. Jerrod