I just thought it was practical. Being able to access the container could come in handy in many occasions. But the truth is that we don't know how the shivan world functions, and so do not know what would make sense for the shivans. They
could have need for large personnel transports or luxury liners (

) for all we know. But we have only seen an invasion army so we have no idea.
Since there was some discussion about the nose I presented a logical idea that came in to human mind. And to me, a door doesn't sound
that out of character, but then it comes to personal prefrence. What we really need, is a Shivan to ask opinion from.
EDIT: But if the door is out of the question, I think the circle with three "eyes" looks best to me...
