the c-gensym2 comes from your $method. There are a couple of ways to get rid of them. Choose the one that suits your needs.

1. Give your method a name:

   my $method = SOAP::Data
       -> prefix ('wkpb-stuf')
       -> name( 'potato' )
       ;
   [download]

   This will generate a SOAPAction: "http://www.vrom.nl/wkpb/stuf#potato" header and the following soap body: <wkpb-stuf:potato>      aanvraag</wkpb-stuf:potato>
2. Use a plain string as method name:

   my $soap = SOAP::Lite
       # ...
       ->call( potato => SOAP::Data->type( xml => $aanvraag );
   [download]

   This will make a SOAPAction: "#potato" header and this soap body: <potato>      aanvraag</potato>

I hope that gives you enough hints to solve your issue.