We had really good sound and no feedback issues at all for the nearly two hours we played, until the very last song. For some reason it decided to go nuts then. Fortunately we were shutting down anyway so we just pulled the plugs, literally, a little early. No idea why it would be fine for so long and then feedback like that, but since that was the only thing that went wrong, we all counted our blessings.
We had a blast again and really felt more comfortable this time.