I'd agree with what Emmerson says - but also the reassurance that in general French roads are much less busy than British roads, and also French drivers are more likely to be overtaking you than letting you overtake them! I know this is a generalisation, and obviously there will be occasions when you need to overtake, but it's not like driving in British traffic.
Time your journeys, too. HGVs are 'off-road' for most of the weekend, except those with refrigerated cargos, so there is also less likelihood of a slow-moving HGV going up the hill in front of you. Also, between 12 and 2 lots of HGVs seem to stop for lunch, so it's a good time to travel (but not a good time to try to find space on a service area to have your own lunch), so eat earlier, and drive through that time. On dual carriageways on hills there is often a slow-vehicles lane, which keeps traffic moving, too.
Your main problem will be drivers seeing a caravan in front and trying to overtake you just as you're pulling out. As Emmerson says, stay well back, and accelerate quickly!