You can fill pvc pipe with cement, or use water jugs. I'd recommend the heaviest thing you can find. Make sure you loop the rope around the top of the frame and not just the legs. I recently had a horrible experience where the wind picked up at a show. My tent went flying, and all of my clothes and signs went flying. We didn't know what to grab first. It was a hard lesson learned and a $140 tent ruined.
I'm wishing you beautiful weather though and lots of success at your show!