Complex Param for SOAP-Call

Hi,
I'm trying to use a webservice, which needs some complex parameter.
The request should look like this:

   <?xml version="1.0" encoding="utf-8"?>
   <soap12:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-
   instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"
   xmlns:soap12="http://www.w3.org/2003/05/soap-envelope">
     <soap12:Body>
          <GetObjectList xmlns="http://www.omninet.de/OtWebSvc/v1">
               <Get folderPath="ChangeMgmt\RFCs" recursive="true">
                    <Filter>demo</Filter>
                 <RequiredField>Title</RequiredField>
                 <RequiredField>Description</RequiredField>
                 <RequiredField>LastChange</RequiredField>
                 <RequiredField>Priority</RequiredField>
            </Get>
       </GetObjectList>
  </soap12:Body>
</soap12:Envelope>

How do I build such a complex request with PHP?

Christian