Preheat the oven to 375 degrees F (190 degrees C).
Combine brown sugar, jerk seasoning, paprika, thyme, oregano, seafood seasoning, and crushed red pepper in a bowl; rub generously all over the tenderloin. Wrap with bacon and secure with toothpicks. Coat lightly with oil and place in a loaf pan or casserole dish. Sprinkle any remaining spice rub on top, cover with some diced onion, and surround with remaining onion.
Bake, uncovered, in the preheated oven until pork is slightly pink in the center, 45 to 60 minutes. An instant-read thermometer inserted into the center should read at least 145 degrees F (63 degrees C).