A more sensible idea would be a heat exchanger in the car heater coolant feed with water pumped through tubing.
So then to drive my heated seats with a PWMing MOSFET via the ESP32 that can handle 2x5A at 12V, do you have a suggestion for actual parts to use?
Therefore in the ESP32 section of my circuit, I will put an 18V TVS diode with a fuse, and a choke, to flatten voltage spikes but to also protect against permanent overvoltage.
You wouldn't use high frequency PWM with a heater
then you don't have to do any switching-loss calculations either
I would think it would be more appropriate to use a swichmode converter rated to 40 V.