Sorry for thread hijacking but I've got some good news to share - my heater saga came to happy ending
A mailman dropped a package at my place today...
I swapped 120V element in and THIS IS IT! Oh, i mean HEAT! It pulls between 8 and 11 amps from 180V battery, depending on fan speed (higher airflow = higher current); with ~2000W this feels like heater now - I mean you feel nice warm air from ducts even though it's -7degC tonight. With previous 230V element current could barely reach 5.5A which translates to ~1000W. It surely made a difference from "no heat at all" state and offered almost comfortable cabin temperature but only when driving in city traffic. As soon as I was on freeway it was getting a bit cold and windows got foggy :/ "Half power" position was of no practical use, now I use it most of the time.
I really recommend 120V elements in conversion with battery voltage <200V.