Then take out the passenger seat and build a fire 
.
A wood stove would be better.
Seriously, electric heaters are a terrible way to generate heat. You'd do better energy-wise installing an A/C compressor on the engine and placing the evaporator in front of the radiator and the condenser in the passenger compartment. The thought of all of it is a bit silly, IMO, when the engine is dumping 1/3rd of it's BTUs as waste heat into the cooling system.
with all of the big truck EGR coolers out there on ebay, i've been contemplating putting one on my car.. it would help heat the coolant up fairly quick, but the whole setup would be quite complex. complex as in the coolant would need to be diverted when the exhaust gets too hot...
as for the 12v 1000 watt heater, that thing is garbage. 120v @ 1000 watt is wayyyy more efficient. i'm still blown away that car manufacturers are sticking with 12v DC. i thought i heard that they were going to 36vdc sometime in the future, and that is a step up, but a real baby step...
IMO, cars should have a 3 phase 1000 watt inverter for 24vdc for things like afterrun rad fan etc, and then simply use the alternator to run everything when the car is on. the efficiency of a/c power is incredible. plus the benefit i like the most, is not needing these huge wires going throughout the whole car. 3 phase motors are very efficient and last much longer and provide higher output than similarly sized DC motors.
a non electronic vw diesel would be a perfect candidate to make the swap to using AC
i wonder what the size of the '09 tdi's battery and alt is? probably 160 amp alt with a ginormous battery... it'll suck for whoever has to replace that down the line
