I am not familiar with the Yamike cargo box, but when I bought my E320T the dealer gave me a catalog of all the original M.B. cargo boxes and sets you can fit to the rails at the roof of the T-series.
Believe me, skies are just one of the hundreds of things Mercedes design the racks to hold. There are a ton of different aerodinamic cargo boxes that attach directly into the rails (they vary in sizes and prices). There are racks for skies (as mentioned) but also for bikes, surf boards, camping equipment and tents, model airplanes, sky gliders, canoes, boats (of all types and sizes), field equipment for surveyors, well, almost everything but the kitchen sink.
All of them are listed as original Mercedes-Benz accessories and some can be even ordered to match your car's color.