fluxbox resize window complete full

If you want to have the resize grip available in the complete bottom edge and not just the corners then edit the file

const int grip_width = 20; //TODO to const int grip_width = m_window.width()/2 ; //TODO

Now there will the resize grip on the complete bottom of the window.

To increase the borderwidth or edge do the following:
name@linux:~ > grep -i width .fluxbox/styles/kde4/theme.cfg
menu.bevelWidth: 0
menu.borderWidth: 1
window.bevelWidth: 0
window.borderWidth: 2
window.handleWidth: 1
toolbar.borderWidth: 1
toolbar.bevelWidth: 1
toolbar.clock.borderWidth: 1
toolbar.workspace.borderWidth: 0
toolbar.iconbar.borderWidth: 1

Dont do this
to increase the thickness of the grip (only to the lower bottom of the window)
Edit: src/FbWinFrameTheme.cc
*m_handle_width = FbTk::Util::clamp(*m_handle_width, 0, 200);


*m_handle_width = FbTk::Util::clamp(*m_handle_width, 4, 200);