Try wxFormBuilder!
https://sourceforge.net/projects/wxformbuilder/
I use codeblocks for my wx-projects, even for development of wxFormBuilder.
Codeblocks is a great IDE, I really like it and the formula codeblocks+wxFormBuilder works very well for me.
Recently, wxFormBuilder 1.0 has been released and a new branch of this project will be started soon. The future of wxFormBuilder will depend on the interest and colaboration of other people into the project. I plan to create a public forum on sourceforge for all kind of ideas, suggestion, design proposals, etc.
I respect to other people who prefer developing another RAD from scratch instead of helping the wxFB development and I would like to say that there won't be any kind of competence with those projects, if you think that wxFB is useful for you, just use it, and if you want, you can contribute. There are many kinds of contributions: comments, suggestions, tutorials, translations (thanks metalogic), bakefiles, etc, etc.
I'd like to finish with some words for Upcase:
I think that your work (wxRapid) is really interesting, a few times you say that you lack of time for your project and I like to know if you would like to discuss your approach for future wxFB releases because I think that "sizer based" and "free hand" approaches could be compatibles.
Regards,
Jos