With my MGF EV conversion, I retained the original heater core and pipes, as I really did not want to dismantle dash to get to heater core. I bought a water heater tank (HV) from friend second-hand and behind firewall, plumbed this into existing water heater pipes. to turn-on I used the demister button which has never been used on my soft-top. Heater works really well and heats up the cabin like traditional MGF heater. But really the best thing I installed was heated seat kit off ebay, it draws very little power and warms up your behind nice and quick, some photos below.