Well, it's like a slow tremolo so you definitely want to alternate fingers. Thumb - Middle - Thumb - Middle is a good general-purpose tremolo fingering. To do this easily, you should pull your thumb a little under the palm, almost touching the middle finger. The wrist should be straight but not rigid. You descend upon the keyboard, leading with the thumb. Then a very slight rise of the forearm should allow you to pivot forward to reach with the middle finger. The wrist may move, but only slightly.
If there are shifting accents, you almost always want to play the strong beat with your "power fingers": thumb or index, and then just roll through the other fingers until you need to start over. Use the index for the accent if you want to use the thumb for backbeat.