Assuming you are paying for the fuel, the bottom line here is what does it cost to generate 1KWh in a car and how does that compare with your local Power cost? I have no data but my bet would be that it is several times more expensive in the car?
A bit of data from the net for a Diesel Generator shows 20KW generator at 1.6 Gals / Hour at full load.
So if we take a Gallon of Diesel at $2 x 1.6 = $3.2 for 20KWh
Off the grid at 10c / KWh = $2 for 20KWh
This is of course for a generator, car could be better or worse? However it's much closer than I expected, so perhaps I have got the data or the maths wrong?
Rich
Diesel I think you have too low. I don't even think you can get offroad diesel for that price. That is first part I would check.
Other thing is cooling how are you going to cool it? Say it's in trunk it might be insulated enough to block noise, but it's going to get hot. And it's pretty hard to do a temporary mod for cooling that is realistic on a car. So I think it still has some problems in idea.