Soak a plank of wood in water for at least an hour. Trust me, if you don't soak long enough you'll run into trouble.
In a large bowl mix together the ground beef, salad dressing, egg, worcestershire sauce, vidalia onion, bread crumbs, salt and pepper. Just mix long enough for it to come together. Never over-mix meatloaf or burgers. Trust me.
Shape the meat into two loaves. I do the shaping right on the planks. It just makes it so much easier.
Place on a medium heat grill, right on the grate. Close the lid and allow to cook for about 30 minutes.
Lift the lid and brush the barbecue sauce all over the meatloaves. Put the lid back down and cook for about 15 to 20 more minutes.
Remove from the grill and allow to rest for about 10 to 15 minutes. Slice it up.