Create an array of Vector3 from Editor script

I'm looking to generate an array of Vector3 using an Editor extension script, then use that generated array in RunTime. As it stands I can generate a array using an Editor script no problem, however as soon as that function completes the array is not "saved" for use in RunTime.

Editor Extension Script

 [CustomEditor( typeof(GridTest) )]
 public class GridTestEditor : Editor {
     
     GridTest gd;
     
     public int gridSize = 10;
 
     // Use this for initialization
     void OnEnable () {
         gd = (GridTest)target;
     }
     
     // Update is called once per frame
     override public void OnInspectorGUI() {
         gridSize = EditorGUILayout.IntField(gridSize);
         if(GUILayout.Button("Generate Grid")){
             GenerateGrid();
         }
     }
     
     void GenerateGrid(){
         gd.gridData.Clear();
         for(int x = 0;x < gridSize;x++){
             for(int z = 0;z < gridSize;z++){
                 GridPoint gp = new GridPoint();
                 gp.position = new Vector3(x,0,z);
                 gd.gridData.Add(gp);
                 Debug.Log(gp.position);
             }
         }
     }
 }

Grid class and GridPoint Object

 public class GridTest : MonoBehaviour {
     
     public List<GridPoint> gridData = new List<GridPoint>();
     
     // Use this for initialization
     void Start () {
         foreach(GridPoint gridPoint in gridData){
             Debug.Log(gridPoint.position);
         }
     }
     
 }
 
 public class GridPoint : Object {
     
     public Vector3 position;
     
 }

On start up the GridPoint objects loose there assigned Vector3

Could anyone point me towards what I need to be doing in order to use this generated array?

Cheers, C.