You say you are cooking a whole tenderloin. Are you going to use it as one piece or cut it in half? Remember, the tenderloin is not uniform in size, end-to-end. I would recommend cutting in half. You will have two different size pieces. Monitor the temp carefully, especially on the smaller piece whiled cooking. Remember to take the meat out somewhat early because the cooking doesn't stop when you pull it off the grill. Good luck and let us all know how it worked out.
Art