The pof exporter is really pissing me off, after crashing max a few hundred times, now it exports the barrels incorrectly (see pic).
It also creates two log files, locks them (so I can't delete them) and appends a few megabytes (23 in my case) to them after each export. A few exports later they are 120 MB large, and for some reason they seem to be kept in memory, so my computer runs out of physical memory and I have to restart Max
I followed the instructions in the readme. The turret bases are named gunturret-x and linked to the hull, named detail-0. The three barrels are one object and they're linked to the bases. The barrels of the smaller turrets are missing because I didn't link them to the bases.
The position of the barrels depends on the main object's pivot point. In this picture, I moved the pivot point to the center of the object before exporting. Before that it was in the front, and the barrels were behind their current position.
Edit: with the original pivot point, marked by the blue cross: