Thanks Rob, VW Transporter plus Aero on the roof comes in well under 3m (circa 2.5m). I frequently use the Grand St. Bernard tunnel when going to Italy as it is cheaper, there are never any queues and from circa early May onwards there is the option of going over the pass. This adds circa 15 mins to the journey but it is spectacular and easily driveable (incl in a larger Motorhome)... but it is also free.
Just be careful to check the height restrictions for the Mont Blanc tunnel. I think with VW van + boat on top you'll still be under 3meters, but as soon as you go over it you are classed as a HGV and pay a huge price to go through the tunnel.
For info in case anyone is still thinking about Sardinia.... a couple of people I have coincidentally spoken to in the last week looked at ferries from Toulon & Nice in France, which seem to be more expensive and have more height restrictions (I have a VW Transporter and my Aero goes on the roof). However ferries from Genoa have much fewer height restrictions, go more often and seem to be cheaper. Genoa is also the same drive time from Calais, you just need to go via the Mont Blanc tunnel or Switzerland (Grand St. Bernard tunnel). Google "Traghetti Lines," there is an option for the wording to be in English.
