Pierce potatoes with fork. Microwave on HIGH 4 to 6 minutes or until tender, turning over halfway through cooking. Let stand 5 minutes or until cool enough to handle. Halve potatoes, then cut into 1/8-inch thick slices. Remove husks and silk strands from corn. Cut each ear into 4 pieces.
Mix butter, lemon juice, mustard, garlic, paprika, black pepper and red pepper in large bowl. Add shrimp, corn, sausage and onion; toss to coat well.
Place potatoes in even layer in 13x9x3-inch disposable foil pan. Top with shrimp mixture. Arrange shrimp so that they are at the top to avoid overcooking. Cover pan tightly with foil to prevent steam from escaping.
Place pan on grill over medium-low heat. Close lid. Grill 20 to 25 minutes or until shrimp are pink and vegetables are tender.