Are there safe places to park a leased minivan filled with suitcases near the Vieux Port in Marseille, so we can stop on our way from Avignon to St. Tropez to take the boat ride to Chateau d'If?

There is no place in France, maybe in all of Europe, where you can park a car full of visible luggage and expect to have the contents still visible in even a few hours, unless you hire a German shephard and put him in the car.

Park in a pay underground parking. They have security and cameras. If possible conceal all items inside. Do not park on the street.

There is a pay parking on side of the vieux port where all the restaruants are... i think thats the south east side.... Look for a large blue square with a white capital P in it.

Do not leave anything in sight, like maps, guide book that points to tourist.

I suppose my question has more to do with whether or not Marseille had parking garages (not unlike Manhattan) where you "pay up" to have your car in a more secure location. If, in fact, these more secure parking areas do not exist in Marseille, then our alternative is to visit 1-2 days earlier - either driving ourselves with no luggage in the van, or 2) taking a chauffeured guided trip with an Avignon-based guide company. Any thoughts here?

Aside from the public underground garages I haven't seen any of the sort you're looking for. Why not get in touch with your car-rental agency and ask for recommendations?

The above posters are absolutely right about leaving nothing showing in the car. All through Provence you will see signs warning tourists not to do so, especially near major sightseeing (and some minor, as the memorial arch outside St-Rémy).