It's taken me a while but I've finally managed to draw up the ship that the food bunker is built on...
The blue lines represent the approximate outline of the food bunker I built (you might need to rotate your screen slightly). The cargo ship shown represents a standard layout but this would be adapted prior to being buried. Some bunkers are essentially just store rooms to protect goods while others are also an automated processing centre where food or other delicate supplies are prepared and suitably stored.