A modular container for maintaining an article under controlled temperature conditions comprising: a generally rectangular box-shaped enclosure defining an interior volume, wherein at least one enclosure side comprises an access opening to allow for insertion or removal of the article within the interior volume, and wherein enclosure sides are made of an insulating material; at least two first phase change elements comprising a first phase change material and disposed within said enclosure, wherein each of said at least two first phase change elements is positioned adjacent one of a pair of opposed enclosure sides; at least two buffer inserts disposed within said enclosure, wherein each of the at least two buffer inserts is positioned adjacent to one of the at least two first phase change elements on an opposite side thereof from the sides of the enclosure, and wherein the at least two buffer inserts are selectively interconnectable with each other to define a larger or a smaller payload volume for the article; at least two second phase change elements comprising a second phase change material and disposed within said enclosure, wherein each of said at least two second phase change elements are positioned adjacent to one of the at least two buffer inserts on an opposite side thereof from the first phase change elements, and wherein the second phase change material changes phase at a different temperature than the first phase change material; whereby the modular container further comprises a centering element disposed within said enclosure, wherein said centering element is positioned adjacent to a side of the enclosure that is perpendicular to an orientation of the at least two first phase change elements, and wherein said centering element is positioned in supporting contact with the at least two first phase change elements so as to support said elements generally centrally along the respective side of the enclosure to which said elements are adjacent. a generally rectangular box-shaped enclosure defining an interior volume, wherein at least one enclosure side comprises an access opening to allow for insertion or removal of the article within the interior volume, and wherein enclosure sides are made of an insulating material; at least two first phase change elements comprising a first phase change material and disposed within said enclosure, wherein each of said at least two first phase change elements is positioned adjacent one of a pair of opposed enclosure sides; at least two buffer inserts disposed within said enclosure, wherein each of the at least two buffer inserts is positioned adjacent to one of the at least two first phase change elements on an opposite side thereof from the sides of the enclosure, and wherein the at least two buffer inserts are selectively interconnectable with each other to define a larger or a smaller payload volume for the article; at least two second phase change elements comprising a second phase change material and disposed within said enclosure, wherein each of said at least two second phase change elements are positioned adjacent to one of the at least two buffer inserts on an opposite side thereof from the first phase change elements, and wherein the second phase change material changes phase at a different temperature than the first phase change material; whereby the modular container further comprises a centering element disposed within said enclosure, wherein said centering element is positioned adjacent to a side of the enclosure that is perpendicular to an orientation of the at least two first phase change elements, and wherein said centering element is positioned in supporting contact with the at least two first phase change elements so as to support said elements generally centrally along the respective side of the enclosure to which said elements are adjacent.