We have done this route for many years heading for a destination just around that coast from you. The deciding factor is what time will you be arriving at Le Havre. If it is an early morning and dependant on your ambitions and driving stamina Cahors on the A20 is possible by 6pm after landing at around 7am. From around there with a 9am start you could be in Begur just after lunch.
If time is no issue Ecommoy just south of Le Mans has a nice municiple, Loches between Tours and Chateauroux for the A20 has a couple of nice sites, Uzerche has a big busy but pleasant site by a lake, Souliac has a few sites, whenever we were near Cahor we never found a space on a site so went to Caussade just down the A20.
I have to say that I have found the A20 route to be a lot more thirsty on fuel when towing than the A75 route which is not as up and down as most people make out.
When you get to Begur if you are after an easy diner one evening give Can Padre (known Chicken & Chips affectionately) on the edge of Pals a go, it gets very busy but after your visit KFC will be viewed as a stinking rip off by comparison. For your drinking needs go to Grau just outside Palafrugell (your side), you can't miss it on the right.