It`s an Intermodal trailer. Under 4.0m high, low-ish floor, and 33euro plt.
The yellow plates are where the crane lift the (whole) trailer up. They sit in the wells of low-loader type rail wagons.
4 bays with the drop sides you can see, wooden or alloy slats above that between the posts. The few straps on the sheet are purely to stop it flapping about too much, nothing at all to do with securing load.
The sliding roof in the one in the pic is adrift from the framework, hence the straps thrown over it, to stop any more damage if wind gets under it.