Unfortunately, Sid only has tint2 version 0.12.12 in the repos; need version 0.14.0 or better (current version 0.14.6) for the buttons and some other features.
So I compiled tint2 from source to upgrade my VSIDO install. -->
EDIT tint2 version 0.14.3-1 is available from experimental repo.VSIDO - fluxbox - tint2; using tint2 buttons with the ~/.fluxbox/apps file:
left click on the terminal button starts xfce4-terminal:

right click on the terminal button starts tmux session in uxterm:

use the ~/.fluxbox/apps file to set uxterm to maximized and border only decor:
[app] (name=xterm) (class=UXTerm)
[Position] (CENTER) {0 0}
[Deco] {BORDER}
[Maximized] {yes}
[Alpha] {255}
[end]
middle click starts a root terminal.
tint2rc button:
button = new
button_icon = /usr/share/icons/Vibrantly-Simple-Dark/apps/32/terminal.svg
button_text =
button_tooltip = Terminal
button_font = Sans Regular 8
button_font_color = #000000 60
button_background_id = 0
button_centered = 0
# horiz vert space icon/text
button_padding = 1 1 2
button_max_icon_size = 28
button_lclick_command = xfce4-terminal
button_rclick_command = uxterm -e tmux
button_mclick_command = `gksudo xfce4-terminal`