$arg = {foo=>{bar=>{baz=>['qux']}},bar=>[bar=>{baz=>'qux'}]}

<s-gensym3 xsi:type="namesp2:SOAPStruct">
 <foo xsi:type="namesp2:SOAPStruct">
  <bar xsi:type="namesp2:SOAPStruct">
   <baz SOAP-ENC:arrayType="xsd:string[1]" xsi:type="SOAP-ENC:Array">
    <item xsi:type="xsd:string">qux</item>
   </baz>
  </bar>
 </foo>
 <bar SOAP-ENC:arrayType="xsd:ur-type[2]" xsi:type="SOAP-ENC:Array">
  <item xsi:type="xsd:string">bar</item>
  <item xsi:type="namesp2:SOAPStruct">
   <baz xsi:type="xsd:string">qux</baz>
  </item>
 </bar>
</s-gensym3>