I don't know anything about commercial PID units, but as a control algorithm I have to think it's overkill for this application. Unless you're going to set up a PWM setup, there's no point using anything other than a basic, linear, thermostat-type controller. Using your 2°F differential, set the target 1°F higher than your desired temp, get a 1-2 kW element and a relay for it to control, and you'll be in business. That's the basic setup we use for temperature control in our 7 bbl brewhouse, and it's all you need.