Preheat oven to 375 degrees F (190 degrees C). Combine cream cheese and mayonnaise in a large bowl and mix well. Add spinach, water chestnuts, bacon, Cheddar cheese, green onions, dill, garlic, seasoned salt, and pepper and stir until well combined. Cut off 1/2 to 1 inch off the the top of the Hawaiian bread to make a lid. Hollow out the rest of the bread to form a bowl. Make sure to leave a little layer of bread throughout the inside of the bowl and save the pieces for dipping. Fill the bowl with the dip and cover with the lid. Wrap in aluminum foil and place on a baking sheet. Bake in the preheated oven until bread bowl and dip are thoroughly heated through, 1 1/4 to 1 1/2 hours.