Thanks all for the responses. Especially Nacho for the diagram.

Think I'm going to try wiring it like Derale suggests, turning on fans sequentially. My main question what temps to turn each fan on/off?

With a 180F thermostat, I'm guessing Fan 1 - On at 185F, Off at 180F, Fan 2 - On at 190F, Off at 185F? I'm just taking an educated guess with those numbers. That's why I was asking you guys.

If this method doesn't work, I'll keep the PWM as Plan B.

Thanks