We all have our own solutions, and when we find one that works, we're religious about it.
You asked for advice, so here's mine. First of all, negative temp anything is really cold. Not sure I'd have the balls to completely shut down, but I don't deal with that cold. Here, we get low, single digits at times, but I still have hard core customers come in. Is it profitable at that time to stay open? Probably not, but in the long run, yes. I don't want customers to wonder whether I'm open or not, thus, I stay open.
I am a hot water weeper down to 15 degrees, then I'm wide open cold water weep. I have temp sensors on the last non moving part of the bay, right on the pipe that feeds the boom. Settings for each sensor vary on the distance to the bay for the hot water to travel, and has taken years of fine tuning.
Even with that, I get an occasional freeze up, but theirs usually a reason such as plugged tip, etc.
This is how I do it. I'm sure there are other ways, but this way is mine. ��