//a serializable class, it should be possible write an custom property drawer for it
[System.Serializable]
public class SimpleClass
{
  public int myField;
}

[CustomPropertyDrawer (typeof (SimpleClass))]
public class SimpleClassDrawer : PropertyDrawer{

    public override void OnGUI (Rect pos, SerializedProperty prop, GUIContent label)
    {
      SerializedProperty myField= prop.FindPropertyRelative ("myField");
      //here's the problem: myField always null
    }

public class Test : MonoBehaviour {
  public SimpleClass s;
}

using UnityEngine;
using UnityEditor;
using System.Collections;


[CustomPropertyDrawer (typeof (ScaledCurve))]
public class PropertyDrawerTest : PropertyDrawer {
public override void OnGUI (Rect pos, SerializedProperty prop, GUIContent label) {
    SerializedProperty myValue = prop.FindPropertyRelative ("myValue");

    int indent = EditorGUI.indentLevel;
    EditorGUI.indentLevel = 1;
    EditorGUI.PropertyField(
        new Rect(pos.x,pos.y,pos.width,pos.height),
        myValue,
        label
    );
    EditorGUI.indentLevel = indent;
}
}

using UnityEngine;
using System.Collections;

[System.Serializable]
public class ScaledCurve {
    public int myValue = 1;
}

public class PropertyDrawerImpl : MonoBehaviour {
    public ScaledCurve Curve;
}