I have done a week charter on one of the many rental boats on the canal. We went from Carcasonne to Narbonne. It was a highlight of my life and we will go back at some point. Supposed to be doable with 1.5 m so 1.2 should be OK. One thing to think about is that the lock walls on the Canal du Midi are not straight, they are sort of arch shaped (remember the thing opened in 1680 and they were making up the engineering as they went). If your mast was substantially longer than your boat (ours is about 15' longer), you would have to be very careful not to have the mast hit a lock wall when the lock was empty and you were trying to leave the lock, e.g., if you get the bow out far enough to clear the lock you might hit the mast at the stern. I was wondering how much you would gain by not having the mast down the centreline of the boat - perhaps have it near the centre at the bow and near the stern quarter so you get more safe swing room. Of course you would have to do all the locks on the same side. Also, absolutely avoid August when the French are all on holiday. We were there in September and about 40% of the charter boats were out and it was busy enough. Can't imagine what it would be like when all the boats are rented.