In the travel industry? No way. We are simply folks who love to travel and manage to do this for about 6 months a year. We have met many travel industry folks over the years, and most have "impressed" me with their lack of personal travel experience. Getting back to Marseille, it can be hard to find the train travel schedules because France's railroad (SNCF) has a confusing web site and not all their routes are listed in major web sites such as RailEurope. The train system that runs out of Marseille into Provence is generally part of their regional rail system called the TER. The trains leave from the St Charles train station which is the main station in central Marseille. I am not sure where your ship will dock, but you probably would have to take a shuttle into town (they would drop you in the old port area) from where you can walk the few blocks to the train station (just ask anyone to point you in the direction of the Gare St Charles). There are usually about 2 trains per hour to Aix and the one-way journey takes 30 - 40 min (depending on the train). From Marseille to Arles takes about an hour and there is usually 1 or two trains per hour. Unfortunately, the train connections between Aix and Arles are not convenient (no direct service) which rules out doing both places on trains. Its one of the reasons that we prefer to have a rental car when in many European ports (including Marseille). There might be some kind of bus service between Aix and Arles, but we have very little knowledge of the French public bus lines. Its about an hour drive between those cities. With a car, there are many nice routes that can take you to places like Aix, Arles, Avignon, Les Baux, and St Remy. These are all great places to visit to get a good feel for the region.
Funny that you mention Garmin Nuvis. We have one (Model 670) which came with the North American and European Maps. We have used it extensively in Western Europe, and it works well except sometimes it does not always give you the perfect route. If your model does not have the European maps (most don't) you probably know you can buy the CD from Garmin and load it into your unit although you might have to add a memory chip. Since the major European rental car companies rent the units for about $15 a day, you can do the math and see if it makes sense.