Prepare the tenderloin by carefully trimming off the fat and the silver skin. Tie up the tenderloin with string to make a roast, coat with olive oil, and season generously with Mansmith’s. Cover with plastic wrap and let the seasoning penetrate the meat for one hour at room temperature.
Heat the entire grill to the highest temperature by turning all of the burners on high for about 20 minutes. Sear each side of the roast to develop the crust, 2 minutes on each side. After the last side sears, turn off all of the burners except the one farthest from the tenderloin, and adjust that burner to medium-low.
Insert a thermometer into the center of the tenderloin and slow roast with indirect heat until the thermometer reads 130 degrees F for medium rare (about 45 minutes). Depending on the thickness of the roast, you may want to cook to 125 degrees F for a smaller roast, or 132 degrees F for a larger one. Do not exceed 132 degrees F as cooking will continue while the meat rests for 10 minutes before slicing.