This may seam like a super silly hack, but might be worthwhile. Consider heating only 1/3 your cabin vs 100% of your cabin. How? Shower curtain!
Place a clear $10 Amazon shower curtain right behind the driver seat with magnets to hold it up. Your cabin will heat or cool in 1/3 the time, and in turn, increase efficiency of energy usage. I’d actually cut it to size so that it is a custom fit end-end without wrinkles or folds.
No seriously, joking aside, I think it might be something to consider for those particularly living in harsh weather.