Ive not been to Sequoia Park, but been many times to sites South of Bordeaux. The most straight forward, particularly with Van in tow is to head from Caen down towards Rennes, Nantes and then Bordeaux until you come to the Signs for Royan around Saintes. There are a reasonable number of stops - though the section from Rennes to Nantes has few - and no fuel I seem to remember.
This is dual carriage/Auto route apart from about the last 50kms and is mainly toll free - the onlt peage is from Nantes south. IIRC it was about