As Simon has mentioned, and do not drive past the check point which is before you get to Frejus, i think it is about 20 0r 30 kms away, in France too.
The paperwork has to be 100% accurate, or you will not be able to proceed, it is a group of Pompiers or firemen that are highly trained in ADR, so you can not pull the wool over their eyes, any discrepencies in the load paperwork and the equipment required , they can call the Gendarmes over to issue a heavy fine, the Pompiers are very serious so not a good idea to make jokes to them.
It is quite easy not to spot the sign for the AdR control point, if you miss it, they will send you all the way back again.
When you get to the tunnel, park at to the right in the ADR parking area, and walk over to the glass window, to present the paper work and the authorisation that the firemen gave you.
You will need to get the ticket for the tunnel before the van convoy escorts you through, some firms fax the payment to the toll booth, and this takes time to find the booking refence and payment information.
I think ADR or the fridge drivers get a free token for the coffee vending machine?