reverse polarity protection using alternative configuration
You have your zener diode connected incorrectly (reason below): -

That's how it should be connected to prevent gate-source over-voltage.
Reason
If you connect it as you originally had it then, when trying to protect against a reverse voltage of 30 volts, the zener would conduct (forward biased) and apply 29.3 volts to the gate. Given the the source would be connected to the negative end of the reversed supply via the load impedance, you could certainly expect damage to the gate-source region. Typical gate-source maximum voltages are around 20 volts.