Preheat oven to 350°. In a small saucepan, cook and stir cream cheese and 2 tablespoons butter over low heat until melted and smooth. , In a large cast-iron or other ovenproof skillet, saute onion, celery and green pepper in remaining butter until tender. Stir in shrimp, crab, soup, rice, mushrooms, garlic salt, pepper sauce, cayenne and cream cheese mixture., Combine cheddar cheese and cracker crumbs; sprinkle over top. Bake, uncovered, until bubbly, 25-30 minutes.