I thought that France was in mandatory lock down with police and army checking the credentials of anyone out on the streets. Even if it were less restrictive in the more rural areas I’m not confident that you would find a site open. So it would be major aires for stop over. Are you with either of the Clubs for your stay as their travel service may help given at this time there must be quite a few Brits heading home from Spain.
Looking at HMGs latest advice there are border checks between France and Spain and you would require a completed Attestation. But travel through France should be permitted.
https://www.gov.uk/foreign-travel-advice/france
IWe drove back from southeast Spain leaving a week ago today and Eurotunnel last monday morning.
The situation is unclear and much of the information wrong and confusing.
All campsites in Spain closed to new arrivals about 12-14th March and some have now started evicting existing residents - some directly and some by progressive closure of toilet blocks etc effectively enforcing the closure.
First overnight was at a truck stop Km 165 on Valencia to Zaragoza autopista , free but noisy. Next day into France on N121A directl back road not the main autoroute crossing. Armed with letter from campsite manager who woud not write that the site was closing but just that we needed to get hoe. I explained to the frontier gendarme that we needed to get to ferry and got waved through in 3 minutes. The big site Rouletta at St Jean de Luz was empty and closed, but I used a very small site near Dax at which we had stayed many times in the past and they made no problem of an overnight. Next night to site near Nantes - very rural and well known to us. Agreed a short stay (2 nights as we needed rest) but said we needed to have 'reason' forms. Theare /were required for all people, showng name age address and 5 tick boxes for justification of travel, none of which actually fitted the circumstances of returning to a ferry to go home. One form for each person, one for each day. Only available then on line which must have been awkward for many elderly French people not on line. Spot fine initially 35 euro rose overnight to 135 euro.
Last night at small site near Boulogne which behaveed basically as if nothing was happening. Not stopped or checked in any way. LucK o f the draw, other friends stopped 3 times. Used autoroutes as much as possible - almost empty but very expensive diesel.
All campsite in France now officially closed. I was able to email the sites I had used beofre in reasonable French which may have helped at bit.
Motorway service areas often had significant food stocks too.
So came home to self isolation but glad to be here. Much less happy with the way the ferry company hnadled the cancellation, see a future posting