SKJay,
Sent you a PM. Coming from the Dutch side, follow out to you climb the hill saying Welcome to the French side just past Cupecoy. Continue to follow the twists and turns through the streets. You will pass by a gaurd gate, but keep going for about another mile or so. As you drive, you will come to a sharp right turn leading to the Sandy ground and into Marigot. Just before that sharp right, there will be an open area with large green waste-bins near the entrance. Follow in and that is the parking area for Baie Rouge.
If you are coming in from the French side, follow out of Marigot and into Sandy ground. Continue to follow the road as it rises up the hill and goes left. Follow the road to the opening directly in front of you just before you are forced left. Have fun when you get there and enjoy the food at Gus' and Chez Raymond. Don't worry about your car, the beach boys in the lot will keep an eye on it.