I haven't had any 'missions' come up for my SWA. I just sink what I can find and it counts towards the tonnage sunk requirement.
If you stay within the whole patrol are you will see activity along the southern coast of Ireland.... just don't be in a big hurry.

Up at the the NE corner to the channel entrance between Ireland and the UK at the edge of SWA, you will see a bit of activity too. In the late night hours of 2/19/40 (22:00) I did raise a rukus with a small convoy to British and Neutral ships along the soughtern caost of Ireland. There were also about 6 British escorts with them to contend with too.