I'm a solo tourer too, and wouldn't have it any other way! I can go where I want, when I want, stop where I want to stop, etc..
Last summer I went to the Loire Valley via ferry to St Malo and train to Nantes, returning from Orleans by train to Caen for the ferry back to Portsmouth. Not once did I encounter any hassle or even unfriendliness. Unless you count the junkie at Rennes railway station who was quite insistent that he wanted a piece of my pizza, until he realised that hungry and angry Scotsmen can be quite protective about these sorts of things. He got the message and left me alone, to go and find himself another victim

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As far as precautions go, I would say there is nothing you need to do that you wouldn't do in the UK.. Get a feel for your surroundings and make a common sense decision as to whether you cannot let the bike and luggage out of your site for 5 seconds; or if you can happily swan off for a wander round town and a leisurely lunch. Obviously don't leave valuables on the bike like passport, phone, or cash. I carried a long security cable and padlock, which I used to thread through the pannier handles and bike frame as well as a sturdy fixed object. Not much use to the determined thief I know, but a deterrent to the casual opportunist while you are having lunch or choosing a bottle of red at the local Carrefour.
I love France and wish I didn't live so far away from the south coast, or I would visit much more often.