Touring in French summer hols?

Banjoplayer

Help please! 
Our annual French tour is usually timed to end by the start of the French school holidays, but this year we have no choice but to travel later. 
One well-known travel guide suggests that campsites are generally full in high summer, and “No-one who values life, limb and sanity should ever be caught on the roads during the last week of July, or August,
and least of all on the weekend of August 15th” !

We’ve never driven through France in August, but surely it can’t really be that bad?