Creating a multiple part turret what locks onto certain axis.

Ok so, I have a game Im trying to work on, the turrets I am using are two parts ( shown in http://puu.sh/6Xg7o.jpg ) and I need to be able to make a " realistic " rotation so that the top part can only rotate up and down while the bottom part only rotates sideways. I know that is quite easy to do, however I also need to make it dynamic so that the turret can be rotated any way, it will be attached to a spaceship which can move upside down or in any direction so I can not just use a " Hacky " method to set the x y z to certain values.

Does anyone have any sources / idea's of how I would achieve this? I have been trying to do this for quite a while today but angles are not really my thing.

Help would be amazing.

Here is the code I am using right now, setting the local version of the rotation messes up when I rotate the turret.

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 public class EntityTurret : Entity
 {
 
     public GameObject target;
 
     public GameObject baseObj;
     public GameObject midObj;
     public GameObject topObj;
 
     void Start()
     {
 
     }
 
     void Update()
     {
         transformTowardsTarget();
     }
 
     int getDir(Vector3 f, Vector3 tD, Vector3 u)
     {
         Vector3 perp = Vector3.Cross(f, tD);
         float dir = Vector3.Dot(perp, u);
         if (dir > 0.0f)
         {
             return 1;
         }
         else if (dir < 0.0f)
         {
             return -1;
         }
         else
         {
             return 0;
         }
     }
 
     int getDirVertical(Vector3 f, Vector3 tD, Vector3 u)
     {
         Vector3 perp = Vector3.Cross(u, tD);
         float dir = Vector3.Dot(perp, f);
         if (dir > 0.0f)
         {
             return 1;
         }
         else if (dir < 0.0f)
         {
             return -1;
         }
         else
         {
             return 0;
         }
     }
 
     public static float SignedAngle(Vector3 v1, Vector3 v2, Vector3 n)
     {
         return (float)Mathf.Atan2(Vector3.Dot(n, Vector3.Cross(v1, v2)), Vector3.Dot(v1, v2)) * 57.29578f;
     }
     
     float getAngle(Vector3 p1, Vector3 p2)
     {
         Vector3 targetDir = (p1 - p2).normalized;
         float angle = Vector3.Angle(targetDir, transform.forward);
         int dir = getDir(transform.forward, targetDir, transform.up);
         switch(dir)
         {
             case -1:
                 return 360 - angle;
             case 1:
                 return angle;
             default:
                 return 0;
         }
     }
 
     float getAngleUp(Vector3 p1, Vector3 p2)
     {
         Vector3 targetDir = (p1 - p2).normalized;
         float angle = Vector3.Angle(targetDir, transform.forward);
         int dir = getDir(transform.forward, targetDir, transform.right);
         switch (dir)
         {
             case -1:
                 return 360 - angle;
             case 1:
                 return angle;
             default:
                 return 0;
         }
     }
     
     void transformTowardsTarget()
     {
         Transform t = target.transform;
         Vector3 p = t.position;
         Vector3 p2 = transform.position;
 
         Vector3 targetDir = (p - p2).normalized;
         Vector3 forward = transform.forward;
 
         Vector3 finalRot = new Vector3();
 
         Debug.DrawLine(p2, p, Color.blue);
 
         float yAng = getAngle(p, p2);
         float xAng = getAngleUp(p, p2);
 
         Debug.Log(yAng + "," + xAng);
 
         finalRot.y = yAng;
         finalRot.z = transform.localRotation.eulerAngles.z;
         finalRot.x = transform.localRotation.eulerAngles.x;
 
         midObj.transform.localRotation = Quaternion.Euler(finalRot);
 
         // ALL TEST CODE BELOW ( For reference )
 
         //midObj.transform.LookAt(new Vector3(p.x, transform.position.y, p.z));
         //midObj.transform.Rotate(0, 90, 0);
 
         //topObj.transform.LookAt(new Vector3(p.x, p.y, p.z));
         //topObj.transform.Rotate(0, 270, 0);
 
 
         //float angle = Vector3.Angle((p - transform.position), transform.forward);
 
 
         //Debug.DrawLine(topObj.transform.position, tO.transform.forward, Color.blue);
 
         // Mid Rotation
         /*
         Vector3 flatVectorToTarget = transform.position - t.position;
 
         flatVectorToTarget.y = 0;
 
         Quaternion newRotation = Quaternion.LookRotation(flatVectorToTarget);
 
         midObj.transform.rotation = newRotation;
         midObj.transform.Rotate(0, 90, 0); // rotate offset to make turret properly face target.
 
         // Top Rotation
 
         flatVectorToTarget = transform.position - t.position;
 
         newRotation = Quaternion.LookRotation(flatVectorToTarget);
 
         Debug.DrawLine(topObj.transform.position, t.position,Color.red);
         Debug.DrawLine(topObj.transform.position, tO.transform.position, Color.green);
 
         topObj.transform.rotation = newRotation;
         topObj.transform.Rotate(0, 90, 0); // rotate offset to make turret properly face target.
         */
         /*
         
         Vector3 point = t.position;
         point.y = transform.position.y;
         midObj.transform.LookAt(point);
         */
         //point = t.position;
 
 
         //topObj.transform.LookAt(point);
 
     }
 
     public override void onEntityInitialized()
     {
 
     }
 
     public override void entityTick()
     {
         
     }
 
 }