Sorry haven't been to the site, but you can find good directions on Geoportail, which gives very detailed maps like our Ordnance Survey.
Here are the directions I worked out from there:
Take the A9 autoroute, exit 36, then the D64 towards Valras Plage, carry straight on past the first small roundabout, take the D37E off the D64, and carry on on the D37E. At a crossroads turn right - my guess is that all the names of the campsites will be signposted here. Most of the campsites are off to the left of this road.
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