There's definitely some slight offset from the middle though when I said make them spin on the spot you can easily do it without my help - just set the unit movement speed to the minimum and have them do it in-game, it the turrets become misaligned then it's not spinning about the middle point of the model (as the turrets always remain in the same distance from this middle point and use the units' facing angle to stay on top of the model) generally speaking the way around it is to either have the model edited, or to simply keep the turrets closer to the middle (the human siege engine model also has this issue) so that they don't visually move around as much or "fall off"