I'm not aware of such a Perl IDE, that would provide both the GUI design and the code editing functionnality :(

On one hand you have code editing tools like Komodo that allows you to "easily" edit/debug Perl projects (there is even a VisualPerl plugin for MS VisualStudio). All the Perl IDE I found with Google are just code editors without UI design support.

On the other hand you have Glade that allows you to design your Gtk UI interface and generate the corresponding Perl source code, then you fill the callback functions with your favorite editor ...

In fact, Perl standard and default UI seems to be STDIN and STDOUT ... that's why there is no RAD tools for Perl :)))