Might be worth bearing in mind that an ICE rejects TWICE as much energy into the cooling system as it actually uses pushing the vehicle along. It should come as no surprise at all that energy consumption fully doubles if it is being run to generate as much heat as an ICE can put out.
Less than double your traction energy usage, which is quite possible in practice without getting too cold, and you should count yourself lucky!
Also to note that li tech doesn't like charging under 0 C. Automotive cells have an improved operating range by virtue of their chemistry and engineering, but the range of temps for charging are still limited. However, when it comes to drawing current, li can be safely used up to a much wider range of temps. So you may well find no imposed limitiations to drawing power at a given temp, but that there are for charging (which might include regen function, as that is also charging, of course). Might also, therefore, be worth charging up as soon as you get home, if you live in a real cold place, while the battery is still warm.
In my opinion, EVs should be fitted with (at least offered with) fuel-burning heaters so as to maintain range during winter. Makes no sense to me whatsoever to burn fuel at a power station, converting only a part of its thermal energy to electricity, send it down power lines, then into a charger with various efficiency losses, same again into the battery, and only THEN use what's left to generate heat! Doh! Renault Kangoo ZE in Europe is offered with a diesel heater, I believe, which some might find a bit smelly but is OK for a delivery vehicle.
Probably best option would be a catalytic heater using LPG. Ultimately, if your winter range is 50 miles which could be extended to 80 with $200 worth of heater, then $200 sounds like a much much cheaper way of improving range than adding $5k of extra batteries! If fuel is used for catalytic heating, it's almost 100% efficient, whereas burn it in a power station and it is probably worse than 25% of its calorific energy gets into the EV battery as useable power, so resistive heaters would be less than 25% and heat pumps are probably around the 50% level. .. Just burn it in the EV instead, at 100% efficiency!!!