If what you have via WWW::Mechanize is good for you thats just fine tho. I just thought you might find it of use to see a more nuts and bolts method of doing it too. A closer to "core" method.

One thing i do like about my method is the dumper file with all of the request, not just the content. It helps in figuring out what is going on. I dont "mech", but a way of changing $mech->save_content("formfile.txt"); to something like $mech->save_response("formfile.txt");, the content is in the response. Related is the ability to rerun off the saved files, so you can fix an intermediate part locally with temporary prints without having to go the the website again.