Custom Editor - Loosing prefab connections at runtime

I can drag a prefab to the empty gameobject slot in inspector fine, but once I hit play the connection is lost.

My editor script looks like this

 [CustomEditor(typeof(IglooCameraController))]
 [CanEditMultipleObjects]
 public class IglooCameraControllerEditor : Editor {
     
     IglooCameraController cameraObject;
 
     public void OnEnable(){
         cameraObject= (IglooCameraController)GameObject.FindObjectOfType(typeof(IglooCameraController));
     }
     public override void OnInspectorGUI(){
             serializedObject.Update();
         cameraObject.cameraPrefab= EditorGUILayout.ObjectField("Camera Prefab",cameraObject.cameraPrefab, typeof(GameObject),true) as GameObject; 
         cameraObject.setVlaues ();
     }
 }

And the IglooCameraController looks like this (I've taken all irrelevant code out)

 public class IglooCameraController : MonoBehaviour {
     
     public GameObject cameraPrefab;
 
 }