Wow wish I was more specific now, don't know just never been there so wouldn't know what to expect so not coastal. Something with a decent size shopping centre and food and drink clean campsite for 20ft motorhome
Municipal sites are usually the ones centrally placed in towns - of the larger towns that applies to sites at Nantes, Quimper, and St Malo. But of the smaller towns then La Roche Bernard, Erquy, Matignon, Roscoff, Lannion and Chateaulin all have sites within walking distance of shops, bars and restaurants . But French motorhomers ignore them all and stay on town Aires in order to be conveniently placed at minimal cost. And of course grass pitches are the norm on French campsites - hard standings are very rare - and for Motorhomes which are big and heavy that is probably another good reason for using Aires rather campsites.
Camping Le Cenic in Penestin, lovely town with a large village feel, great outdoor markets and a supermarket within walking distance of the site and beaches if you want a short drive/longer walk/easy bike ride
Don't forget to leave a review of the French and other European campsites you have visited!
Carnac or Trinite Sur Mer so that could be Camping la Baie, Camping La Plage, Camping Kervillor, Camping le moulin de ???? Camping les menhirs or La Grande Metarie, most of these are reviewed on my profile.
Carnac Plage is a really lovely town, nice cafes, shops great beaches.
highly recommend
Was going to suggest Les Sables Blancs myself (as did MrDasherD above). Concarneau is a very nice town and the camp is 1.5km walk from the old town centre. Concarneau also has numerous shopping complexes (eg Decathlon, Intersport, Mr Bricolage, hypermarkets, etc) a few km drive away on the town bypass.
Although you said not coastal, tbh most of Brittanys main towns are on or near the coast (Carnac, Vannes, Lorient, Concarneau, Benodet, St Malo, etc) The 2 main ones that aren't are Quimper (which has a municipal, but personally I would be wary if there are no reviews somewhere of it) and Rennes (which is huge and doesnt seem to have any camping near the centre anyway).
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.