Hi Percy
We've been through the tunnel twice. First time a puncture meant we arrived at c teatime on the first Friday of August, going south. Long delays so we went over the St Gotthard Pass. We were towing a caravan but the pass was well engineered with reasonalbe hairpins up and down and a flat plateau like stretch in the middle. If your tow car is up to it I would recommend that if you experience long queues. The Pass is a turn off the main road through the tunnel.
I must confess that I'm not too fond of tunnels especially ones as long as the St G.
I've just noticed the date so I may be too late for you. I'm posting this from a wifi centre in the French Pyrenees.
Regards
Tim