A sort of circular cell “large enough to cram two Fox shuttles in.”
The cargo ferry is operated by a recessed wall console (via tentacle).
Once the spiral hatch is closed, during transit, it sounds like multiple heartbeats coming from all around and the floor vibrates before there is a slight sensation of horizontal linear motion. The Cargo Ferry can take a zig zagging path through the bowels of the vessel.
Source: YSS Sakura Mission 7 Part 2