Interesting point I have done it for a few years and only had interest. However I have only used big sites and the wardens don't pay the electric bill. I don't use electric for anything else (except Fridge) as I have Led lights and Solar - enough to charge the tablets and power the TV tuner.
Some one Vacuuming a caravan or a fan heater in an Awing users a lot more power than a charge. Different people use their quota different ways.
You could hide it, park close to the van and use the van connecting lead behind a chair. etc,
Do Not connect direct to you van electrics, they are not designed to supply 10 amps for a long period and the cabling tends to be a bit thin for my liking. The 16amp Orange cable is fine.