Driving through the Caitlins for three days next month. Where should I stay as a base?

Depends on what you want to do. There are two distinct parts of the Catlins, the North (which is rather confusing, as technically, its east), and the South. We've based in both on separate trips as we wanted to explore each area in depth.

Here's a map that might help you narrow things down.

https://www.whistlingfrogresort.com/...guide-map.html

We once based in Fortrose, and once about 20 minutes south of Owaka.