Actually I had envisioned underside turrets to work just like they do now; they face backwards and straight down normally. So to make a forward facing one with a -10 degree elevation with one of those, you'd use the settings
+ default rotation 180
+ default elevation 10
Actually to make the model most convienent to what it's defined as in the actual pof, default elevation should be 0 for straight up/straight down and every point up to 90 adds a degree of rotation from normal. It's less clean from the table writer's perspective, but it's closer to what we already have.