The WildCamping.co.uk location app has a good range of aires and wilding spots in France and
www.campingcar-infos.com/view.php is another very good resource.
I have seen suggestions that it can take some time getting through border control at Ouistreham (or Caen as BF insist on calling it). Could be worth looking at ferries from Poole or Portsmouth to Cherbourg as well. BF have a couple of crossings late in the week doing one Portsmouth/Cherbourg rotation with their ferries used on the service to Spain. Prices on those crossings from Cherbourg to Portsmouth appear to be quite competitive versus other BF central Channel crossings. Outbound, however, they are overnight services, so you have to factor in the cost of a cabin or reclining seat.