Bigtop and Gantry provide limited support for rpc style SOAP.
There is a small but complete working RPC style SOAP example in the RPCSoap subdirectory of the keyword_cookbook directory. See the README in that directory for how to run the working example.
namespace_base is used by Gantry in WSDL generation.
it is everything after http: or https: in the prefix for all sorts of names.
See wsdl.tt in Gantry's root directory for which names it affects.
Build the example with
bigtop -c example.bigtop all
Change to the new Kids directory and look in lib/Kids/GEN/Soap.pm for 'soapstuff'.
NOTE: the example in this directory lacks the code needed to make a SOAP server respond to requests. For that see the RPCSoap subdirectory of the keyword_cookbook directory.