You double your journey time on the nationals, It sucks. I prefer to pay the tolls and get there quicker, even in a van. Also, on the autoroutes you are less likely to be robbed if you stop to sleep at a service station than if you just pull over on the side of the road.
One thing to keep in mind about travelling in france during the summer, never travel on a Saturday. It’s the day that gite rentals start and end and the holiday destination roads (a9, a7 etc) are always gridlocked. Red or black warning signs at the payage entrance means slow or stationary traffic on the autoroutes.