Charge 15E for the cost of it.
On top of the camping permit you have already paid for?
Don't give them ideas
On the pass question, they can be fine, or very funny about it, have experienced both.
2 years ago they let Andy in and out all week without checking his pass, and spent the first 4 days checking my pass every time I came back in.
The odd thing was his bike is fitted with panniers and top box and mine isn't.
They obviously didn't like the look of me.