You could try 'locate gtkmm-2.0' but on my system it didn't turn up anything. Google is your friend:
http://sourceforge.net/projects/gtkmm/
Checkinstall should take care of it. I haven't really used swaret.
But you don't really need fluxconf. Fluxbox has up to five text files in ~/.fluxbox that you can add to the menu like
[exec] (fluxedit) {gedit ~/.fluxbox/menu ~/.fluxbox/init ~/.fluxbox/keys ~/.fluxbox/slitlist ~/.fluxbox/groups}
or
[exec] (fluxedit) {gvim -S ~/fluxedit.vim -geometry 109x43+0+14}
(after opening the ~/.fluxbox directory in gvim and saving it as a session).
Voila! A better, more complete, more consistent fluxconf. I don't even know what fluxbg is.
Fluxbox is my favorite window manager and, on the stripped-down side, I doubt you'd find better, but it's a personal choice. If you want more, you want something else, probably.
--- And if this isn't your actual question I'm going to shoot myself. I've been spectacularly dain bramaged lately.