Soak the tenderloin overnight in a mixture of salt water with brown sugar (3 tbsp salt per quart of water, and however much sugar you want) This step doesn't add much flavor, but it produces meat you can cut with your fork. Remove from water and pat dry. I make a rub with the following:
brown sugar, cajun seasoning, garlic powder, fresh ground black pepper, ground rosemary, and a little sage. Rub the mixture on, and let it sit in the fridge for a few hours. I grill it using the indirect method for about 25-30 minutes or until the internal temp is around 150 degrees. Its the best I've tried.