
I've not used one at 3 co's before but it's usually £5 which goes towards the rescue society running it, there are usually benching in the tent but also spaces for cages.
I've been there when the shows open approx 7.30 and the tents were manned then.
As the unentered tent is in the car park you won't need a removal pass like the one for the show but you should get a peice of paper like a receipt from the person at the tent so you show them that when you come back to the tent to take the dog.
Also remember water & a bowl for the dog :)