''southern'' France ...3 options

Salut Bucephane! Comment ca va? - I would choose option 3 for the France leg. Marseille is a wonderful city and there are several places nearby you can visit with so much activities to do. Are you planning to be in that portion of your trip for 5 nights only?

Bonjour/Hi !
Of course 5 nights isn't much. We dont want to see/do Provence (we keep that for another trip).

If you aim to go to Provence at a later time, I would skip option 3.
Also, you can take your French car to Spain, do the Spain part of your trip, then finish back on the French side.

As an example, you could start in Bordeaux, go to Arcachon, Saint Jean de Luz, then cross into Spain. Bordeaux could be a day trip from Arcachon, to minimize changes of hotels.

And on the way back from Spain, assuming you cross into France from Aragon, you could go to the Cauterets area (Pont d'Espagne and Gavarnie are beautiful), then head to Toulouse or Bordeaux again for the flight back.

Why not fly into France and out of Spain, rather than double back?

Why not fly into France and out of Spain, rather than double back?

You need to return the car in France. It makes sense in your case. it is fairly easy to plan a C-shaped route in Spain that would bring you back to France without doubling back the same way, anyway :-)

Hi,
A side comment here, referring to your Spain bit. I guess that you have read the Rick Steves book, hence Segovia as well as Madrid. Last September on our Spain/Portugal trip trip we drove from Madrid to Segovia - but the highlight was stopping at The Valley of the Fallen and El Escorial on the way. You possibly already have this in your plan and it would be easy to visit these two places on the Segovia. We stayed the night at El Escorial but you wouldn't need to (we're a bit older and slower now!). Segovia doesn't need long, we walked through the town and visited the castle mid-late afternoon then went to the Cathedral in the morning before we headed off. We did go to the Ingresia de Vera Crux (fabulous Knights Templar round church that you can see from the castle) on our way driving out of Segovia.

Back on topic... Carcasonne is fabulous. It must be hideously busy now (first went in 1991, stayed a night, magic. Returned for a couple of hours in 2005 with daughters - good, but busy) so you you can do an overnight there that is perfect.
On our Spain and Portugal trip, we did lots of research (initialy triggered from this helpful forum) and we found the best option was to rent a one-way car in Spain, got ourselves over the border (mydaytrip.com, expensive but way cheaper than keeping the car, could have taken a train or bus) then a one-way car in Portugal.
You could fly in to France and out of Madrid.
Happy planning