Unit48.com is an Australian subsidiary of the Dutch based Unit45.com container company. In association with Freightquip Australia, they now provide both curtainsided and drybox 48' units for the Australian market. Unit45 is Europe's leading innovator in the creation and manufacturer of container solutions.
In Europe, where the 45' unit is more common, as it provides better specifications in the loading of pallet cargo, while here in Australia the 48' is more common.
I first saw a photo of one on Wagonfreak's blog back in June. A chance today, to get out and see 7MP7 Trailerail, and there they were. About 10% of the train.