Bring a large pot of salted water to a boil and cook macaroni noodles until they are al dente, meaning they still have a bit of chew and texture.
Preheat your grill to 225˚ F using a mild hardwood--like cherry or apple.
Heat a 12 inch cast iron skillet over medium heat. Melt 1/2 cup of butter and whisk in the flour until a smooth, thin paste forms. Then whisk in the mustard powder.
Carefully pour in the half and half and bring to a boil while whisking. Reduce the heat and whisk in the cream cheese until smooth.
Whisk in the cheddar cheese and Gouda cheese and stir until melted. Turn off the heat and pour in the cooked macaroni noodles. Stir gently until the noodles are coated by the cheese sauce.
Combine the melted butter, sweet rub, and bread crumbs in a small bowl. Sprinkle over the top of the mac and cheese.
Place the skillet in the smoker, close the lid, and smoke for 1 hour. You can smoke for up to 2 hours if you want a stronger smoke flavor, but the noodles will take on quite a bit of smoke fairly quickly.
Serve your Mac & Cheese warm while the cheese is nice an melty!