I would use a contactor. I would wire the contactor ahead of everything but the PID. That way, when the control panel is plugged in, the PID will be on but all the power beyond the contactor will be off until you turn it on. You can monitor temps or set up your PID with the elements off. You could also switch your pid if so inclined.
Is your 20 amp 240 vac outlet 4 prong or 3 prong? If 3 prong, you will need a contactor with a 240 vac coil. See below
If 4 prong, you can use a contactor with a 120 vac coil
The contactors have male quick connects that you can use to wire the switch to the coil and to wire the PID. Very clean and very simple. Some would disagree, but with the contactor as a mechanical shut off for the element, you could safely use one SSR to control the element. The mechanical shut off is very convenient to prevent boil overs.
I would also buy a power cord with a GFI unless your 20 amp, 240 vac breaker is a GFI breaker.