Preheat an electric smoker to 225 degrees.
Cook the macaroni in a large pot of boiling salted water per the package directions.
Meanwhile, in a 10-inch cast iron skillet over medium heat, melt 4 tablespoons butter. Add the flour and stir with a whisk until no lumps remain. Cook for 1 minute, stirring constantly.
Gradually add the milk and heavy cream, stirring until the mixture is smooth and slightly thickened. Stir in the dry mustard, salt, and pepper.
Remove from the heat and stir in the shredded cheese until smooth. Drain the macaroni and add to the skillet, stirring until evenly coated.
Melt the remaining 2 tablespoons butter. In a small bowl, stir together the panko breadcrumbs, bacon, and melted butter. Sprinkle this mixture evenly on top of the macaroni and cheese skillet.
Transfer the macaroni to the smoker and add wood chips (hickory or apple) to the wood chip loader. Cook for 1 hour, until hot through and through.