We have done various bits of the route, non-toll, over several years. From Dunkerque we've used the D300, to the St Omer by Pass, then headed towards Bethune, Douai, Cambrai, St Quentin, where we've actually towed right through the town without problems. We then take the D1 to Chaugny Ternier, Soissons, Chateau Thierry, Montmirail, Sezanne, Troyes, then the D671 down to Dijon. The above route is all fine, quite straightforward, and with no particular hold-ups, though obviously takes longer than the autoroutes! In parts it takes you right alongside the Seine and there are some nice places to stop for lunch. There are plenty of municipal campsites in the villages along this route - the one at Couchy le Chateau in the northern part of the route was very 'atmospheric' - full moon, howling dog in the chateau.....................! The only campsite we've been disappointed with was at Darois, just north of Dijon - lovely pitches, but expensive for what it was! (Some years ago, though)
From Dijon we've used the D974 down to Beaune, and then the N6 down the side of the autoroute, until Macon where we've crossed the autoroute on to the D306. This takes you to just north of Lyon, where you can jump on the free autoroute to get you through Lyon, then we come off again at Vienne just before the toll section, back on to the N7 which continues almost down as far as Avignon. In the Rhone Valley the non-toll route is slow and in some parts you go through quite narrow sections in village centres where there are chicanes. Again there are plenty of sites. We used to just find a site when we were ready to stop.
We've also driven down the Route Napoleon - when we stayed near Castellane we cut off the corner, instead of going down the Rhone Valley we did Grenoble, Sisteron, Digne, Castellane. To be honest I don't remember much about the drive down to the Mediterranean from Castellane, though we did do it, except for the traffic jams in Grasse - and the smell of perfume which pervaded the town.
We may be back in that area again this year, we haven't been for a while now as we've tended to stick to the western side of the Rhone in the last three or four years. We'll probably base ourselves somewhere east of Avignon, in the Vaucluse area - we love the lavender Plateau de Valensole, and that area has some wonderful places to visit. We stayed at Regusse, and did some organised walks from the campsite - but I couldn't replicate them, we just followed the guide!
You can walk in the Gorge du Verdon - but it's serious walking, not a scenic stroll. There are lots of guide books available on Amazon and like sites, if you want 'holiday walking' rather than a long-distance walk.