Hello Alwyn..
As your dog has to be treated by a vet not more than 48 hours nor LESS than 24 hours prior to leaving France, you will almost certainly have to spend the last night on a local campsite - so where's the need to have access with the van?
We stay on a site at Pernes les Boulogne where the owner of the site ( himself a farmer ), arranges for the dog to be dealt with by a local vet who operates from home so parking is a doddle.
His house is only about a quarter of a mile from an enormous hypermarket so you can do all of the last minute shopping at the same time and the Tunnel is only about half an hour away up the motorway.
Take a look at .
http://www.caravancampingsites.co.uk/france/62/senlecques.htm
Hope this helps,
Olly.