A storage module adapter assembly includes adapter base plates that are two-person portable, can be installed/removed by hand, and cooperate with existing structures of existing modular cargo containers. Each adapter base plate includes various longitudinal and transverse frame members, as well as first and second longitudinal frame members on opposed sides thereof. The first longitudinal frame member has a first height, and the second longitudinal frame member has a second height, which is greater than the first height. Each of the first and second longitudinal frame members also include generally horizontal flange members extending from a top side thereof, such that when two adapter base plates are appropriately positioned side by side, the generally horizontal flange members on the adjacent sides of the two adapter base plates overlap due to the difference between the first and second heights. The adapter base plates can then be connected together by appropriate mechanisms.