You can use polybar as well in Openbox. The standard panel in ArcoLinux is tint2 but you can replace this.
We edit the autostart file in folder ~/.config/openbox.
sh ~/.config/polybar/launch.sh &
These lines came in with the update of the package : arcolinux-openbox-configs-git and it is saved in your /etc/skel. You need to copy/paste it to your home folder or compare differences with meld.
Log out and back in to see polybar at work.