I think most of the information needed has been posted here already.
Make sure your truck is running at no more than 4m high.
If you plan on using Mont Blanc tunnel, you’ll need to have Euro 3 or higher truck and don’t forget to stop at the checkpoint before the tunnel, past exit 21, to get you check ticket and emissions sticker. Not sure if there is also a euro limit at Frejus.
Most race trailers have low belly lockers, I always raise my trailer suspension (and Unit if a low ride) before going onto the ferries and take it steady, over the ramp, also ask for lower deck if on a cross channel ferry, they’ll normally already have booked you on it but I’ve had a few times recently where they’ve put me in a lane for the upper deck.
Study mr gringe’s route especially the last bit into the park, there is only one road I know to get into it with a truck and that’s the one he has on his route, but it is actually a side street and when you can go no further, as it becomes a one way street going the other way, you turn right into the park, you’ll need to be Well over to the left for the turn. Then follow the road through the park until you get to the circuit entrance.
Through the gate and follow it down until you get to the tunnel under the circuit on your right, it’s a bit steep so if you have a low trailer you’ll need to lift the suspension again to climb up from the bottom.
You can use a credit card to pay for French and Italian tolls and fuel if you don’t have a fuel card that you can use in Europe, so make sure you have plenty of credit on it if you do.