Add/Change in your tint2rc -
panel_dock = 1
to put tint2 in the fluxbox slit (dock). That should keep it visible when you iconify everything to show the desktop. In the fluxbox configuration menu, configure the slit to be where you want your tint2 taskbar to be - bottom left looks like in your screenshot.
You'll may only be able to do this with one tint2 configuration so the tint2 panel with the systray and battery meter will get iconified - you can try putting them both in the slit and see if they auto resize or something.
Probably want to start yourself a general help fluxbox thread and move out of the feedback section at this point.