Right here goes
First I would bypass Paris big style especially if he does tow
A216, 62100 Calais on E15 [Rocade Est] (North)
onto A26 Omer / Lens / Arras / Lille Par Lens / Reims-Paris
onto A4 [E50]
onto A26 [E17]
onto A5 [E17]
onto A31 [E17]
onto A6 [E15]
onto A7 [E15]
onto A9 / E15
Arrive A9, 66480 Le Perthus
SUMMARY
Driving distance: 770.9 miles
Driving time: 11 hours, 25 minutes
That's the route I'd take especially because I'd have the caravan on the back, I know it's longer than your friends
BUT no periphique Phew!!
It is how ever an easy route with plenty of areas to stop and eat in relative safety but not camp over night anymore
I would possibly stop off at one of these on the way
http://www.camping-lyon.com/lyon_campsite.htm
http://mppie.chez-alice.fr/index.htm
http://www.campingfloral.com/prestationUK.htm
Firstly I have NOT visited any of them. I found them due to them being open all year. I would use one out of the Camping Cheques book as that's what I'd be using to pay with