The Opto 22 SSR you picked switches AC to the load and it is controlled by an AC voltage, so you are OK there. Your load won't draw a lot of current, so the relay should also be fine on that account.
The possible problem is that the controller specifies a Minimum amount of load current; it is intended to drive the coil of a mechanical contactor directly. I'm afraid that when the controller is Off, the 'leakage' current through the output 'contacts' of the Watlow will be enough to keep the Opto 22 SSR turned on.
If that happens, you can solve the problem by placing an additional load across the SSR control terminals to make it 'appear' to require more current. Place something like (close to in value) a .1 microfarad, non-polarized capacitor with a voltage rating of at least 300 volts between terminals 3 and 4 of the Opto 22 relay, and everything should be good.
Dr. Tom (Opto 22 Sr. Tech Advisor)