A combination trailer is provided that includes a rear self-discharge trailer having a bottom surface, a front portion, a back portion, and two opposing side panels. The side panels of the combination trailer have a height that is less than the height of the front portion. An enclosure system is also included in the combination trailer and selectively covers an open top of the rear self-discharge trailer. One or more one locking pin assemblies are also included in the combination trailer and are attached to at least one of the side panels of the rear self-discharge trailer such that the locking pin assemblies can be used to secure the enclosure system in a desired position.