Custom Editor Script resets values on Play

Alright, this has been driving me nuts.

I've worked with Unity for years, but this is the first time I've ever really made an Editor script. After scrounging around the internet, trying to sift out outdated code and whatnot, I made a script that I can use to specify Ranges (I know a Vector2 would work, but I have plans for this script). However, when I hit play, any values entered in the Inspector reset to 0 (or a default value). What am I doing wrong?

 using System;
 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 #if UNITY_EDITOR
 using UnityEditor;
 using UnityObject = UnityEngine.Object;
 #endif
 
 [System.Serializable]
 public class Range<T> where T : IComparable
 {
     T _min;
     T _max;
 
     public T Min
     {
         get { return _min; }
         set { _min = value;  }
     }
     public T Max
     {
         get { return _max; }
         set { _max = value; }
     }
 
     public Range() {}
 
     public Range(T min, T max)
     {
         if(min.CompareTo(max) > 0)
         {
             Debug.LogError("Error: Range " + min + " is greater than " + max);
         }
         this._min = min;
         this._max = max;
     }
 
     public bool Contains(T value)
     {
         return value.CompareTo(this._min) >= 0 && value.CompareTo(this._max) <= 0;
     }
 }
 #if UNITY_EDITOR
 public abstract class RangeDrawer<T> : PropertyDrawer where T : IComparable
 {
     [SerializeField]
     private Range<T> _range;
     private bool _Foldout;
     private const float kButtonWidth = 18f;
 
     private static readonly Dictionary<Type, Func<Rect, object, object>> _Fields =
         new Dictionary<Type, Func<Rect, object, object>>()
         {
             { typeof(int), (rect, value) => EditorGUI.IntField(rect, (int)value) },
             { typeof(float), (rect, value) => EditorGUI.FloatField(rect, (float)value) },
             { typeof(string), (rect, value) => EditorGUI.TextField(rect, (string)value) },
             { typeof(bool), (rect, value) => EditorGUI.Toggle(rect, (bool)value) },
             { typeof(Vector2), (rect, value) => EditorGUI.Vector2Field(rect, GUIContent.none, (Vector2)value) },
             { typeof(Vector3), (rect, value) => EditorGUI.Vector3Field(rect, GUIContent.none, (Vector3)value) },
             { typeof(Bounds), (rect, value) => EditorGUI.BoundsField(rect, (Bounds)value) },
             { typeof(Rect), (rect, value) => EditorGUI.RectField(rect, (Rect)value) },
         };
 
     private static V DoField<V>(Rect rect, Type type, V value)
     {
         Func<Rect, object, object> field;
         if (_Fields.TryGetValue(type, out field))
             return (V)field(rect, value);
 
         if (type.IsEnum)
             return (V)(object)EditorGUI.EnumPopup(rect, (Enum)(object)value);
 
         if (typeof(UnityObject).IsAssignableFrom(type))
             return (V)(object)EditorGUI.ObjectField(rect, (UnityObject)(object)value, type, true);
 
         Debug.Log("Type is not supported: " + type);
         return value;
     }
 
     private void CheckInitialize(SerializedProperty property, GUIContent label)
     {
         if (_range == null)
         {
             var target = property.serializedObject.targetObject;
             _range = fieldInfo.GetValue(target) as Range<T>;
             if (_range == null)
             {
                 _range = new Range<T>();
                 fieldInfo.SetValue(target, _range);
             }
 
             _Foldout = EditorPrefs.GetBool(label.text);
         }
     }
 
     public override float GetPropertyHeight(SerializedProperty property, GUIContent label)
     {
         CheckInitialize(property, label);
         if (_Foldout)
             return 51f;
         return 17f;
     }
 
     public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
     {
         CheckInitialize(property, label);
         position.height = 17f;
 
         var foldoutRect = position;
         foldoutRect.width -= 2 * kButtonWidth;
         EditorGUI.BeginChangeCheck();
         _Foldout = EditorGUI.Foldout(foldoutRect, _Foldout, label, true);
         if (EditorGUI.EndChangeCheck())
             EditorPrefs.SetBool(label.text, _Foldout);
         if (!_Foldout)
             return;
         position.y += 17f;
         T value;
         EditorGUI.BeginChangeCheck();
         value = DoField(position, typeof(T), _range.Min);
         if(EditorGUI.EndChangeCheck())
         {
             _range.Min = value;
         }
         position.y += 17f;
         EditorGUI.BeginChangeCheck();
         value = DoField(position, typeof(T), _range.Max);
         if(EditorGUI.EndChangeCheck())
         {
             _range.Max = value;
         }
         property.serializedObject.ApplyModifiedProperties();
     }
 }
 #endif
 
 

And, for the curious, here's how it's used:

 public class SomeClass : MonoBehaviour {
     [System.Serializable] public class floatRange: Range<float> { }
 
     [SerializeField]
     public floatRange range;
 }