I haven't made a meatloaf on the smoker in several years. This spring may be a good time to try it again.
One I make in the oven is Paul Prudhomme's Cajun Meat Loaf. Uses beef and pork, plus lots of veg and spices.
It's fantastic, especially if served with his Very Hot Cajun Sauce for Beef (you can adjust the heat; the orginal is indeed very hot). Recipes for both are all over the web.
It requires a lot of chopping and measuring prep to make both, so set aside some time. It helps to prep the ingredients for both together and put them in separate cups or bowls. "Okay, I need this much onion for the meatloaf and that much for the sauce. Now the bell pepper."