You've described exactly my plan: Use the Watlow as a control for a solid-state relay, which sees the current drawn by my fan. I have plenty of thermocouple wire, which I have attached to the Watlow and confirmed it is working. I'm not sure what you mean by setting the AC to the lowest setpoint possible.
Also, while it would certainly be overkill and impractical, I would love to use PID output to control the fan. The problem is that I have no idea how!