I use a standard refrigerator control thermostat from Grainger, but I've never liked it because it has a 5? on-off variance. I have to set it to 35? to make sure it comes on before it freezes, and then it won't shut off again until it gets above 40?. It's reliable but very wasteful. If we had the cold winters like Michigan I'd have done something else a long time ago.
I use a Dema O473P (Normally open) 120V solenoid, which you can get from
Kleen-Rite for $52.24. The diaphragm type are less likely to stick open than the plunger type, which I've had fail after just one year. I prefer normally open so if your power fails due to an ice storm, your weep will come on. I'm not sure if the Weep Mizer has outputs for a normally open solenoid, but you could add a relay if it doesn't.