Trailoring in France on the Autoroute is super easy. We use a toll tag which reduces the delay at tolls. We plan one over-nighter on the way down to avoid the kids getting too bored and frustrated.
I read up on what the lake police ask for (ICC, insurance, saftety kit etc), purchased all the equipment and passed the ICC test. However, when I go to visit the lake police to pay for the permit, they only ask for the cash.
The permit for Lacanau is based on engine cc, not sure about Hourtin. Take a look at this
link