Cherbourg to Benodet

There is no such thing as 'a Caravan Club site' in France.  There are sites, varying from smallish sites but with good facilities, to all-singing all-dancing large commercial five star sites, offered in the Caravan Club site booking service, and then there are sites run by Caravan Club members.  The lattter are generally smaller sites, but usually have more facilities than you would find on most CL's.  

Le Hallerais is one site offered by the Caravan Club booking service, about half way (or just a little more) into your journey.  It's actually a municipal site (run by the local Mairie or Town Hall), and is near the town of Dinan which is well worth a visit.  I'm nt sure whether you can just book for one night through the Caravan Club, but if not you can book directly with the site, or depending when you're going, just turn up and find a pitch.

However, with a motorhome in France, you can also choose to stay on 'Aires de Service Camping Car' - which are parking areas for motorhomes to overnight, usually with EHU and water (perhaps metered) or sometimes with a toilet and shower facility too.