Tinman, thanks for explaining thus far. If I am correct that R2/R3 creates a voltage divider which reduces the gate potential on the MOSFET to approximately half what the switched voltage is, then I have to make sure that the Zener is rated for at least that voltage. So, assuming 30 Volts max, I need at least a 15V D2, right? If it is only there to protect the MOSFET gate against overvoltage and transients then there is no reason to go with the 18V version since the MOSFET can tolerate up to +-20V (VGS). Have I understood that correct?