在C#中是否有更好的方法形成soap请求?

这是有效的吗?

  XmlDocument doc = new XmlDocument();
     doc.InnerXml = @"<?xml version='1.0' encoding='utf-8'?><soap:Envelope
                 xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance' xmlns:xsd='http://www.w3.org/2001/XMLSchema' xmlns:soap='http://schemas.xmlsoap.org/soap/envelope/'>
                 <soap:Body><Authenticate xmlns='https://na.ntrsupport.com'>
                 <IdOwner>99999</IdOwner>
                 <Login>MyLogin</Login>" +
                 "<Pwd>myPass</Pwd>" +
                 "<PwdInterfaces>interfacePass</PwdInterfaces>" +
                 "<Platform>domain</Platform>" +
                 "<H>" + getMd5EncodedHash(NtrHash) + "</H>" + 
                 "</Authenticate></soap:Body></soap:Envelope>";

我刚刚收到一个未定义的错误从网络服务返回。。。