Maybe your XPath queries aren’t bringing back anything. Have you tested them? You can use the XPath tool that I mentioned above. Just run the tool, open the SOAP envelope file, paste the XPath into the tool, and test the XPath.
By the way, it is not necessary to create the envMessage to use the xpath() function. You can run XPath directly against the inMessage. However, the envMessage may have distinguished fields for the header and body. If so, it might be easier just to use the distinguished fields to get the header and body data than using xpath().