Stir together butter, shallot, parsley, dill, lemon zest, and 1 tablespoon of the Old Bay seasoning in a medium bowl until well blended.
Combine potatoes and water in a medium-size microwavable bowl; cover with plastic wrap. Microwave on HIGH until tender and a knife can be inserted easily in center of potatoes, about 5 minutes. Drain and let stand 5 minutes.
Preheat a grill to medium (400°F to 450°F). Cut 12 (12-inch) square pieces of heavy-duty aluminum foil. Place 6 squares of the foil in a single layer on work surface. Divide potato wedges and corn evenly among foil sheets. Top each with 4 shrimp and 4 clams. Top evenly with sausage slices and lemon wedges. Dollop each with about 1/4 cup butter mixture. Top each with 1 thyme sprig, and sprinkle each with 1 teaspoon Old Bay. Top each with 1 foil square, and crimp all sides to seal tightly.
Grill packets, covered, until shrimp are done and clams open, 8 to 10 minutes, rotating packets on grill halfway through cooking time. Discard any clams that do not open. Serve with grilled French bread.