As you will quickly realise, motorhoming is very popular in France, perhaps partly because of the law that permits people to park off-site. This popularity means that off-site parking areas get very popular in the summer months, as do official campsites (where if travelling in July August peak it’s recommended to book in December!).
The best time of year to camp can often be September and October. It’s our favourite time of year on the Riviera as the weather is generally lovely- although the storms sometimes arrive in October and you’ll want somewhere nice and protected to park up then. Be aware that the coast road between Nice and Cannes can sometimes shut in places with waves crashing over it in the big storms- you may be forced onto motorways and into official campsites at this point so keep your eye on the long-range weather forecast.