Hi Geoff. Basically, I agree with you, but this also applies to things other than heat. Modern vans have much more electric equipment than ours ever did, and whilst I also agree that their usage is for shorter time, nevertheless, the total power used is probably about the same. As you know, I'm no electrical expert, but I would think that an evening's colour tele viewing is probably the same as running my small radiator? I don't have a microwave, or electric kettle or DVD pl;ayer. I do have a fridge and battery charger, and yes, one of the radiators is on all night in the winter. The use of meters would be much fairer, but as you say, the cost of installation would have to be met somehow.
As for using gas heating overnight, we have done this on occasion, but it's a b*gger when the gas runs out in the middle of the night!
I suppose I could by heavier sleeping bags...................