I’m giving somebody a bit advice to get to Monza,
anyway due to the trailer height they are going to use the Frejus tunnel.
I’ve been trough there for a few years and can’t remember if you need to go through a control point, like Mont Blanc
Or if you need to stop somewhere to get a Euro emmisions sticker?
Try reading this FREJUS TUNNEL
Not too many brits like it used to be going through there.
On the way up you pick up signs for trucks which go into a big parking area, this is where you go to get your emissions sticker or when the weather means they park you up.
After that you are free to run up to the top and through unless you have ADR on.
If ADR you will see sign’s at one of the peage’s and you need to book in there and they will send you up from there.
Hope this may help.