Google Earth is useful for checking out those small roads you might be considering in street view and "fly-through" mode. Morgans (as we know!) love small roads but when they are just a bit too rough.. then you might start dreaming about suspension upgrades etc!

I drove up from Avignon on small roads a couple of years ago: never a motorway in sight and very little traffic - just a matter of spending time choosing the route.

1. Map.
2. Google Earth.
3. Sat-Nav and off you go!

Have a lovely trip.. it's a wonderful driving country. Not sure where you live, but you could avoid coming back through France by going over the Pyrenees (amazing!) to Santander and then the ferry back to Plymouth (very civilised). There's always Morgans on that ferry for good reason!
Oliver S.