Parsing Rss/Opml DateTimes

I have been fighting a bit with how to "correctly" parse DateTimes from RSS & Opml feeds. After much wrangling, I decided to go with the most strict form of parsing, whereby I assume the datetime is in RFC822 or RFC1123 format.  

My Opml library uses Serialization, so I use the following technique for Serializing/Deserializing DateTimes:

    /// <summary>
    /// Indicates when the document was created
    /// </summary>
    [XmlIgnore()]
    public DateTime DateCreated
    {
      get{ return _dateCreated;}
      set{ _dateCreated = value;}
    }

    /// <summary>
    /// Indicates when the document was created
    /// In Universal Time.
    /// </summary>
    [XmlElement("dateCreated")]
    public string DateCreatedUT
    {
      get
      {
        if (_dateCreated == DateTime.MinValue)
          return String.Empty;
        else
          return _dateCreated.ToUniversalTime().ToString("r");
      }
      set
      { 
        DateTime tmpDate = DateTime.MinValue;

        if (value.Trim() != String.Empty)
        {
          try
          {
            // Ty to parse as an RFC1123
            tmpDate = DateTime.Parse(value, CultureInfo.InvariantCulture.DateTimeFormat, DateTimeStyles.None);
          }
          catch
          {
          }

        }

        _dateCreated = tmpDate;

      }
    }

I store the DateTime internally in a LocalDate format, but Serialize/Deserialize it as UniversalTime.  As a result, I run into two problems. 1) What do I store if DateTime parsing fails? (I chose DateTime.MinValue), and 2) What should I return if the DateTime value is invalid? (I chose String.Empty)

There must be a better way...any suggestions?