Multipart turrets can be any shape and geometry you want, but they must follow these simple rules:
1) They must have a rotating base subobject
2) They must have a rotating arm subobject set up as a child of the turret base (a direct child mind - not a child of a child or anything else)
3) The centres of the subobject are what the turrets rotate around.
There is more to it than that if you want to have them rotating around an axis that is not the in-game Y axis (topside to belly axis), but as long as you follow those rules then you can make multipart turrets look like anything you can think of geometry and texture wise.
