Unfortunately, the carpet will only absorb high frequencies, which will tend to make low and mid frequency problems more apparent. But it sounds like that decision has already been made.
Muslin is not fire-proof, and will not pass code for a public building. You must use a real acoustic fabric with an A fire rating.I was hoping to be able to pass two washer backed bolts through the 703 and then cover the front face with muslin, wrapped around to the back and glued on. Then, use some as yet undetermined method to attach them to the wall.
The simplest way to attach fabric-covered panels is with impailing clips. They can be mounted to the wall with molly bolts, and they have little sharp knife-like projections that stab into the fiberglass and hold it in place.
Less important than for a small room, but you still want to balance the absorption across the frequency range. That's why the carpet has me worried.How important is bass trapping for a room this size?
If you're not sure about these sorts of structural issues, it may be time to hire a professional.How well with the 703 stay up without a frame?For installation in public spaces, 705 is usually the answer due to it's rigidity.Is 703 good enough? Ethan seems to favor 705FRK for it's accelerated LF absorption.