One of two in the first try, selected "character" boats and was given a chinese Shang west of cuba and a russian Akula on the east. Put the Akula in a direct route to Miami until the depth floor was of 300ft, and then plotted a route along the continental shelf; maintaining roughly the same depth all along. Put her on creep speed, nap on the floor depth, and let her be. The nearest sonobuoy was detected at 20nm and had no contacts at all until arrived the target zone.
The Chinese boat did the same along the Mexican coast, but was sunk when passing under the nose on the Southern base by an air launched torpedo. Given that I never heard any sonobuoy nearer than 60nm I'm fairly sure that it was one of the Orion catching her with MAD when taking-off or returning to base. The Akula, having a non-magnetic Hull (they are made of steel, aren't they?) was invisible to that type of sensor.
So, all considered, fairly easy, I could probably also entered with the Chinese boat if I selected a route along the Cuban coast, since with a week of time there was no motive for me to go faster than creep. And that made me next-to-invisible to passive sonar.