Buying petrol on a Sunday morning in France

PeggyGT

In July we will be sailing overnight from Portsmouth to Caen arriving on a Sunday morning. We will then be travelling on to the Dordogne. Are we likely to encounter any difficulties obtaining petrol on  a Sunday morning in a petrol station large enough to
accomodate our largish tourer ?  When we were ther last year we noticed that many of the petrol stations were not open early on.