Not to be contentious, but I feel the most efficient place for the ceramic heater in back on the shelf.
Folks have a difficult time getting it into the dash, then worry about fire hazard. And even then, the ceramic heater doesn't fully heat the EV and you're still cold in the winter. My friend had to hold his ceramic heater up to the windshield to defrost it.
We got sick of it and developed our own model Inline Water Heater (for sale) that uses the vehicles existing liquid heating hoses and climate controls. For $335, it's simple to install and natural to use. You'll find the EV heats up as warm as an ICE vehicle. Check it out on our website:
Inline Water Heater