In 2-quart saucepan, heat 2 cups water and the salt to boiling over high heat. Add potatoes; heat to boiling. Reduce heat to medium; cover and simmer 5 to 7 minutes or until tender; drain.
Heat oven to 400°F. Spray 11x7-inch (2-quart) baking dish with cooking spray.
Meanwhile, in heavy 3-quart saucepan, cook bacon over medium heat, turning occasionally, until crisp. Remove bacon; crumble and set aside. Using wire whisk, stir flour into bacon drippings. Gradually stir in clam juice, whipping cream and onion salt. Heat until thickened and bubbly, stirring constantly. Stir in potatoes, bacon, peas and carrots, corn and thyme. Cook 3 to 4 minutes longer or until hot. Stir in shrimp and crabmeat. Spoon mixture into baking dish.
On lightly floured surface, unfold pastry. Roll into 12x8-inch rectangle. With sharp knife, cut slits in pastry to allow steam to escape. Place pastry in baking dish over hot seafood mixture. Roll outer edges of pastry over edges of baking dish, and press onto edges.
Bake 30 to 40 minutes or until crust is deep golden brown. Let stand 10 minutes before serving.