We usu. put the Tara weight of a 20" ctr. on 2.200 kgs.
Width varies between 240 and 250 cm.,
What makes them awkward to transport on a flatbed trailer without "twistlocks" is securing them - you def. don't want them to move. Also, they don't like to be transported on their floors - they sit on their corners.. They tent to be a bit tail heavy - the doors are more metal.. Also, the police will want you to have mirrors that look rearwards alongside the container as required by law. We have used reverse camera's in the past but some LEA will not like that.
Have you got something to unload the thing ?