The Peages in France generally have one gate set at 3m to accommodate Cat 1 convoi exceptionnels. If you are running as a Cat 1 convoi (ie anything over 2.55m wide or 4m high), you will need a Cat 1 permit, 4 x marker boards with outline lights and amber beacons and "convoi exceptionnel" boards front and rear. You are also restricted on which roads you can travel on and the times you are allowed to drive. In summary, if you can get the width down to below 2.55m, it is a lot easier and cheaper.
I do a lot of driving in France and the rest of Europe with both Cat 1 and Cat 2 loads, so happy to answer any questions.
South West Boat Transport
Professional Boat Transport across England, Wales, Scotland, Europe & Scandinavia. Any boat up to 50ft.