Abstract: A method of assembling a truck includes assembling a cab structure that includes a rear roof rail coupling a top portion of a rearmost left pillar to a top portion of a rearmost right pillar to cooperate with the rearmost left pillar and the rearmost right pillar to at least partially define a rear opening of the cab structure. The rear opening extends in a vertical direction of the cab structure from the rear roof rail downward beyond a vertical midpoint of the rearmost left and right pillars. The method includes inserting first interior components through the rear opening into an interior of the cab structure and attaching the first interior components to the cab structure. The method includes attaching a rear panel to the rearmost left pillar and the rearmost right pillar after attaching the first interior components to the cab structure, the rear panel spanning the rear opening.