hiya we also use to use a patio heater and battery operated lights but we have ehu now. its not very lightweight with having the gas bottle unless you are taking it with you anyway for cooking and the batteries were costing a furtune bought rechargeable ones then just forgot to recharge them before we went so in the end ehu was the best option for us.
get yourself a florescent tube that will run from the cigar lighter in the car, they are only 8w and consume less than an interior light in a car.
Heating wise how about a black cat heater, they are catalytic so dont produce a flame or one of those heaters that slot onto the top of a suitcase cooker.
If you want the best performance then the best answer is a coleman petrol lamp various sizes to suit needs and a heat/light output that has to be seen to be belived far out performs gas