SettingsRegister(object o);

SettingsFetch(Type t);

class SettingsCollection
{
        [XmlElement("Settings")]
        public List<object> objs = new List<object>();

        [XmlIgnore]
        protected List<Type> types = new List<Type>();

        public void Save()
        {
            XmlSerializer serializer = new XmlSerializer(this.GetType(), types.ToArray());
            FileStream fs = new FileStream("configs\\settings.xml", FileMode.Create);
            serializer.Serialize(fs, this);
        }

        public bool Register(object o)
        {
            Type t = o.GetType();
            if (types.Contains(t))
                return false;

            objs.Add(o);
            types.Add(t);
            return true;
        }
}

<?xml version="1.0"?>
<SettingsCollection xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <Settings xsi:type="MainFormSettings">
    <Kuuuh>kuscheln</Kuuuh>
  </Settings>
</SettingsCollection>

public static SettingsCollection Load()
{
   SettingsCollection  retval = null;
   try
   {
      XmlSerializer serializer = new XmlSerializer(typeof(SettingsCollection));
      using(FileStream fs = new FileStream("configs\\settings.xml", FileMode.Open))
          retval = (SettingsCollection)serializer.Deserialize(fs);
      foreach (object o in retval.objs)
         retval.types.add(o.GetType());
  }
  catch {
  }
  return retval;
}