In reply to Ewan2010:
I've dossed in the car park at Sabot many a time and it seems fine, but for a week you'd need to find some showers etc… there is clean public loo in Milly but you’d be better booking into a campsite every couple of nights. Avoid La Musadiere (sp?) campsite if you are on a budget as it’s rather expensive.
Toll is 20.20EUR if you come from Calais and turn off at the Milly exit of the A6 (Peage starts again just after). Toll is worth it to avoid painful alternatives. If money is that tight then try squeezing an extra person in the car or driving at 58mph
You could take food from UK if you are driving but you’d be better off stocking up with beer in the supermkts in Chailly-en-B or Milly.