Fill a small pot with a tight-fitting lid with about 2 inches of water and fit it with a steamer basket. Turn the stove on to high, and once the water starts to boil, turn down to low, put in the potatoes, and cover. Cook until tender when pierced with a fork but still holding their shape, 10 to 14 minutes (depending on size). Remove and cut into 1" bite-size wedges.
Meanwhile, cut 8 large pieces (about 14-16″ long each) of foil and lay them out double stacked perpendicular (forming a plus sign ) to start 4 grill packets. At this point you can line them with parchment paper if desired—simply put a single layer on top of the foil.
Evenly distribute the shrimp, sausage, potatoes, corn, and onion onto each stack of foil and somewhat “flatten” out the contents for even cooking.
Sprinkle each packet with 1 teaspoon of the Old Bay Seasoning and 1/4 teaspoon of the salt. Lastly, drizzle each one with a little olive oil or add a few small pats of butter.
Carefully bring together the two ends of the bottom piece of foil so the edges meet at the center. Fold the two edges together over at least three times. Then rotate and fold over the edges on the open sides (onto itself) at least two to three times and crimp those together with your fingers as well. If you are throwing these onto the campfire coals (directly over the fire is not recommended) you do not want any chance of ashes making their way inside!
Place the packets in the coals of the fire or on an outdoor grill for 10 - 15 minutes (or in a 400 degree F oven for 35 to 40 min) until the shrimp is pink, firm, and cooked all the way through. Carefully let the steam out as you open each packet and serve.
Dairy free if olive oil is used rather than butter.