Custom Editor for Monobehavior with custom property not retaining Gameobject references

I am writing my own custom editor for a gameobject

 [Serializable]
 public class GameObjectPODO {

 [SerializeField]
 public GameObject Model;
 [SerializeField]
 public string DisplayName;

 public GameObjectPODO(GameObject theModel, string displayName) {

     theModel = Model;
     DisplayName = displayName;
 }
 }

 public class ObjectViewer : MonoBehaviour {

 /// <summary>
 /// The models that are hooked up to the system
 /// </summary>
 [SerializeField]
 public List<GameObjectPODO> Models = new List<GameObject>();
 }

In the custom editor, I click and drag a gameobject into a property field and it gets added to the system as follows

     GameObject newModel = null;

     newModel = EditorGUILayout.ObjectField ("Add New Model", newModel, typeof(GameObject), false) as GameObject;

     //if they dragged a model in and it isn't contained in the previewer, add it
     if (newModel != null) {

         GameObjectPODO newModelObj = new GameObjectPODO(newModel, newModel.name);  //PROBLEM HERE
         _previewer.Models.Add(newModelObj);
      }

But the gameobject reference that I make with the new instance of GameObjectPODO gets lost and is turned null after the object is created.

Can anyone shed some light on this?

Thanks in advance