Mix garlic powder, onion powder, salt, and black pepper together in a small bowl. Spread over baby back ribs. Cover with plastic wrap and refrigerate, 8 hours to overnight.
Place plank on a rimmed baking sheet and pour in enough water to cover. Let soak before grilling, about 1 hour. Drain.
Preheat an outdoor grill to about 500 degrees F (260 degrees C). Place plank on the grate and heat until slightly blackened, about 5 minutes. Flip plank and place ribs on top. Lower heat and cover the grill. Cook ribs, sprinkling some water on top every 30 minutes to create steam inside the grill, until tender, about 3 hours.
Uncover grill and increase heat to high. Brush barbeque sauce over ribs. Cook until ribs are dark brown, about 2 minutes.