I have been watching a YouTube video of Kiwi Rail trains out of Dunedin and at the end of some of the consists are some carriages I have never seen before and I was wondering if someone could tell me what they were and what they were carrying. They are a box car like shape with an orange covering (a tarpaulin?).

Have a look at https://www.youtube.com/watch?v=l_klzlFtGps

Thanks for your help.