In a pot of salted water, cook macaroni until tender, about 8 - 10 minutes.
Preheat oven to 350. Lightly butter an 8 x 8 baking dish and set aside.
In a large sauce pot, add the butter over medium heat. Add the flour and cook, stirring for 2 minutes. Using a whisk, slowly add the milk and cook until it thickens.
Remove the sauce from heat and mix in the cream, paprika, cayenne, salt and pepper. Add 3/4 of the cheese. When the macaroni is cooked, drain it well. Add to it, the shrimp, crab and basil and gently add the white sauce. Spoon macaroni mixture into the prepared baking dish.
Top with the remaining chedar and parmesan cheese.
Bake for 25 - 30 minutes or until the top is lightly golden.