Topeak BackLoader Seat Post Mount Bag 10L Black. The Topeak BackLoader is a large capacity seat bag specially designed for bikepackers providing a streamlined way to carry gear without the need for a rear rack. Constructed of lightweight highly water resistant and durable materials it mounts and removes quickly. The upgraded saddle mount system in conjunction with compression straps reduces the pendulum effect associated with large rear payloads providing a comfortable ride for those long miles. An easy access waterproof inner bag is included to keep contents completely dry.