We haven't stayed at Royat - I think it's a new site to the Camping Cheque network, but we may pay it a visit soon, as it's just in the area we tend to stop overnight. There used to be a CC site at Parentignac, 'La Grange Fort', just south of Clermont Ferrand, and we used that a few times - but it's now become 'Touring Cheques' or ACSI instead. We've also stayed in the municipal at Issoire, or just a bit further north at St Pourcain sur Sioule (which we also stayed at several times) or Chatel de Neuvre (campsite sign has a frog advertising it, but can't remember the name today, sorry). We chose these sites because they are all really near to the autoroute (or the main road in the case of St Pourcain or Chatel de Neuvre)and very easy to find.
Some friends of ours stayed at Camping de la Filature at Ebreuil - and liked it there, but we haven't stayed there ourselves. Other people recomment the site Clos d'Auroy at Orcet (at least I think that's the one).
Recently we've taken to stopping a bit earlier in the day, staying at Camping de Nevers a bit further north again. We're off again in four weeks, and haven't yet even begun to think where we might be heading!