Editor extension, How do I Serialized nested class?

What happen is that My script use lots of nested Class. I was trying to use SerializedObject but without success. How do I show nested class properties on the Inspector?

 SerializedObject.Update 
 //Plenty of InspectorGUI
 SerializedObject.ApplyModifiedProperties 

Wanted to do something like above.

///////////////////////////////////////////////////////////////////////

[Below] Current Code

 using UnityEngine;
 using UnityEditor;
 using System.Collections;
 
 [CanEditMultipleObjects]
 [CustomEditor(typeof(Unit))]
 public class UnitEditor : Editor {
     
     Unit thisUnit;
     
     string unitName;
     UNITCLASS currentClass;
     
     UnitIntVal HP;
     UnitIntVal AP;
     
     void OnEnable ()
     {
         thisUnit = (Unit)target;
     }
     
     public override void OnInspectorGUI()
     {
         
         UpdateProperties();
         
         EditorGUI.BeginChangeCheck ();
         PropertiesDrawer();
         if (EditorGUI.EndChangeCheck () /*&& thisUnit.thisClass.currentClass != currentClass*/)
         {
             DoIfPropertyChanged();
         }
     }
     
     
     ////////////////////////////////////////////////////////////
     void UpdateProperties()
     {
         unitName = thisUnit.GetName();
         currentClass = thisUnit.GetClass();
         HP = thisUnit.GetHP();
         AP = thisUnit.GetAP();
     }
     
     /////////////////////////////////////////
     void PropertiesDrawer()
     {
         DrawNameProp();
         DrawClassProp();
         DrawHPProp();
         DrawAPProp();
         
         DrawDefaultInspector();
     }
     
     //////////
     void DrawNameProp()
     {
         unitName = EditorGUILayout.TextField("Name", unitName);
     }
     
     void DrawClassProp()
     {
         currentClass = (UNITCLASS)EditorGUILayout.EnumPopup("Class", currentClass );
     }
     
     void DrawHPProp()
     {
         HP.valMax = EditorGUILayout.IntField("MaxHP", HP.GetValMax());
         
         HP.val = EditorGUILayout.IntSlider( "HP "+HP.GetVal()+"/" +HP.GetValMax(), HP.GetVal(),0,HP.GetValMax());
         GUILayout.Space(5.0f);
     }
     
     void DrawAPProp()
     {
         AP.valMax = EditorGUILayout.IntField("MaxAP", AP.GetValMax());
         
         AP.val = EditorGUILayout.IntSlider( "AP "+AP.GetVal()+"/"+AP.GetValMax(), AP.GetVal(),0,AP.GetValMax());
         GUILayout.Space(5.0f);
     }
     
     /////////////////////////////////////////
     void DoIfPropertyChanged()
     {
         thisUnit.SetName(unitName);
         thisUnit.SetClass(currentClass);
         thisUnit.SetHP(HP);
         if(HP.valMax < 1) HP.SetValMax(1);
         thisUnit.SetAP(AP);
         if(AP.valMax < 1) AP.SetValMax(1);
     }
 }

////////////////////////////////////////////////////////

 using UnityEngine;
 using System.Collections;
 
 [System.Serializable]
 public enum UNITCLASS{ TROOPER, SENTINEL, STRIKER, LAST };
 
 [System.Serializable]
 public class UnitClass {
     
     public UNITCLASS currentClass;
     
     public UnitClass()
     {
         currentClass = UNITCLASS.TROOPER;
     }
     
     public UnitClass( UNITCLASS newClass )
     {
         currentClass = newClass;
     }
     
     //////////////////////////////////////////////
     public UNITCLASS GetClass(){ return currentClass; }
     public void SetClass( UNITCLASS newClass ) { currentClass = newClass; }
 }