See also LXDE on Slax for the whole desktop environment.
FYI, it appears that Blackbox is available by default.
1) get it
\slax activate openbox
This gets dependencies! Yay!!
xwmconfig and configure the window manager to be xinitrc.openbox-session
3) edit ~/.config/openbox/autostart
you probably want something like
xterm & firefox & lxpanel & dolphin &
4) exit x with C-A-backspace
5) Menu > Session Type > Custom
6) log back in as user root password toor
If you reboot, this system will now autolog into Openbox.