I'm not sure if this helps but in my system I have to transmit , receive and process the raw XML data within the Body of the SOAP packet:

my $response = $service->transport->send_receive(
    envelope => $envelope
);
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Where the $envelope is the XML I have created (This is the whole thing, envelope/head/body).

I also have to deal with multiple attachments and had little luck getting SOAP::Attachments to work with the Sun Java libraries. I just used Mime::Parser and determined the content type, parts (etc)

my $entity = $parser->parse_data($response);
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You can then do this:

        # We have some parts - one XML at least
    my $num_parts  = $entity->parts;

    # No guarantee of order 
    for(my $i = 0; $i < $num_parts; $i++)
    {
        my $part = $entity->parts($i);
        if($part->mime_type eq 'text/xml')
        {
            # Do stuff with XML
        }
        else
        {
            $datatype = $part->mime_type;
            # Do stuff with attachment
        }
    }
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I hasten to add I didn't like the fact I couldn't use a SOAP::* module but I had immense difficulty (at the time) getting SOAP::Lite and Sun to play together anyother way (this was a year ago btw).