Mix the brown sugar, 2 teaspoons sea salt, paprika, cumin, 1/2 teaspoon black pepper, cayenne pepper, garlic powder, and sage in a small bowl. Pat the pork loin completely dry with paper towels. Rub the mixture onto the pork loin to coat completely.
Pour the olive oil into a large resealable plastic bag. Add the seasoned loin to the bag and seal. Allow to marinate in the refrigerator for 24 hours, turning the bag once to assure an even flavor.
Place the red potatoes, sweet potatoes, carrots, and onion in a large pot and cover with water. Add the 2 tablespoon salt, 1 teaspoon pepper, and cilantro to the water. Bring to a boil, reduce heat to low and allow to continue on a slow boil for 25 minutes; drain, reserving the water.
Preheat an outdoor grill for high heat and lightly oil grate.
Remove the pork loin from the bag. Sear on the preheated grill, 4 to 5 minutes per side; remove and set aside. Reduce grill heat to medium.
Place a 12-inch cast-iron skillet on the grill. Lay the apple slices on the bottom of the skillet. Pour the orange juice and lemon juice into the skillet. Place the pork loin on the apples. Arrange the drained vegetables around the pork loin. Pour reserved water into the skillet to fill within 1/2 inch of top.
Cook on grill for 1 hour, pouring more of reserved water over the pork after 30 minutes.