Abstract: A plurality of payload containers are assembled from modularly extendable base plates, and standardized side walls and covers; each base plate has a trapezoidally cross-sectioned trough-like guide channel and includes centrally positioned counterplug means for providing mechanical electrical communication and thermotechnical connection; a payload container fastening plate is provided with corresponding and matching trapezoidally cross-sectioned ridge-like extensions received by the troughs in the container bottom plates for guiding, indexing and heat removal; and plug means extend from the trapezoidal ridges for plug connections with the counterplugs.