Add Openbox session to Xubuntu

Collected notes and Walkthrough - how I did it.
 
For help and info, excellent places are: Crunchbang forum and Openbox Wiki.

I already had configured / tweaked Xfce side of Xubuntu - so 'restricted extras', Icedtea etc were already installed, as were done other 'first things'.

In Xfce session, open your terminal and type:
sudo apt-get install openbox obconf
Logout and login to new Openbox session.
What you find is black, empty screen. It is like that - so fearlessly right-click on blackness, open terminal and continue:

sudo apt-get install menu
cp /var/lib/openbox/debian-menu.xml ~/.config/openbox/debian-menu.xml
cp /etc/xdg/openbox/menu.xml ~/.config/openbox/menu.xml
cp /etc/xdg/openbox/rc.xml ~/.config/openbox/rc.xml
openbox --reconfigure
# previous part installed debian menu and copied all 
relevant menu files to your home.
# now, install also Openbox menu editor
sudo apt-get install obmenu

Take a look at your ./config/openbox/rc.xml - there are various parts of interest; like key and mouse bindings, general window conf and reference (a must) to menu.xml file. Investigate.
Then open up menu.xml - either in freshly installed obmenu or in editor. That's almost empty too! Right, it is - and you can proceed now in several ways:
1. Create new menu section from debian-menu (where things are distributed in most bizarre way). Re-arrange items to their proper places in the menu. It takes time..., --reconfigure often and take a look what happens - copy/paste errors are easy to come.
2. There are menu-related pipemenus in Openbox Wiki. Unfortunately I didn't install them but, maybe they are of help when creating your menu.
3. I took most of menu from my installed Vsido (tweaked already, of course, according to my installs/uninstalls), and pasted it into new menu.xml. Had to make some 10 corrections in items (no sweat). Also, I had 'iconified' whole Vsido menu before (2-3 hours of hard work), I really didn't want to do that again...
Syntacs for adding icons: item icon="/home/yourname/.icons/themename/apps/iconname.png" label="Appname".
Simply add your icon=absol.address into item tags. Easy, but yes, it takes time.

It's reasonable to pair your menu-building with installing - so you don't forget what you added.
1. Things to add what should have been already installed in Xfce (here are also things I personally like and install - question of choice):
synaptic, spacefm (a file manager better than Thunar, has to be taken from here), medit (an editor better than Leafpad), xfce4-terminal, xfce4-taskmanager, icedtea, bum (Bootup Manager, lets you add and remove early startup things), bleachbit (cleaner), gdebi-gtk (might be already installed out-of-box), gparted.
2. Install now: gtk-chtheme and/or lxappearance, update-alternatives, xxkb (how to here), volumeicon-alsa (if going for alsa).
Additionally: ipkungfu firewall (how to), maybe clamav+clamtk antivirus - to be in safe side with usb-s. Also - for more nerdy pro-look: htop. And for syncing and backups and creating your own distro: gsync, fsarchiver, remastersys (looong and complicated theme, do google).

When finished with menu - to great satisfaction and even greater relief, start with other bits of desktop: open ./config/openbox/autostart and start-up some more apps.
Install: tint2 (panel, if one doesn't want to use already present Xfce-panel), nitrogen (wallpaper manager), conky (fancy graphical systeminfo on desktop), compton (compositor). They all have manual config editing only, but there are lot of tutorials/help available.
Config files go: ./config/tint2/tint2rc, ./config/nitrogen/nitrogen.cfg (I think it was auto-created), .conkyrc, .compton.conf. It's probably best to find those files in web and then tweak them according to your fancy. I, again, ripped them from my Vsido installation.
Then you have to stick proper commands to autostart file. Here is one autostart which has almost all included - tweak and shape it according to your situation. Both Tint and Conky take -c parameter for pointing to conf file, like:
(sleep 1s && -c ~/.conkyrc_upleft) &
So you can make several conf files and switch between them.
Spacefm can be started as daemon (helps start speed, with mounting and unmounting and whatnot): spacefm -d. Or, it can be used as (minimal) desktop manager.
For Conky you probably have to install lm-sensors (terminal command is 'sensors', by the way).
Logout/login... ? Sure, everything looks good and somehow more presentable. That's it for first phaze.

Now, what else to install? Openbox themes, of course. Which are easily tweakable... gcolor2 helps to find new exciting colors. Crystalcursors? Suckless-tools to go for more nerdiness?
Or, more practically, wicd (network tool) and/or samba (network tool for linux+windows mixed)?

One more interesting thing to do. Let's make Main Menu to launch from Tints' Launchers and let's make sure that right click on desktop opens our whole menu.
Your rc.xml has to have, and sorry - I can't show xml here, whole thing goes crazy... :
keybind key="A-C-q" with menu-def root-menu.
And also mousebind action="Press" button="Right" with menu-def root-menu.
Now install: sudo apt-get install xdotool wmctrl
Create a folder ./config/tint2/.tint2launchers. Create launchers you want to appear in your Tint launcher there (copy them from your .local/share/applications). Only one that really has to be created is your menu.desktop:

[Desktop Entry]
Type=Application
Encoding=UTF-8
Name=Openbox Menu
Exec=xdotool key ctrl+alt+q
Icon=yourfavoritemenuicon.png
NoDisplay=false

Edit tint2rc file: there has to be 'L' in panel defs block (L=Launcher); and under Launchers block: launcher_apps_dir = /home/yourname/.config/tint2/
It's also possible to use a launcher-script for more 'docky' behaviour. 
And with the same method you can create missing 'show desktop' launcher-icon (exec=xdotool key super+d)

Additionally: Read about relations/fixes of Compton and multimedia. 
I tend to remove pulseaudio, and install alsa only. How to here. 

AND FINALLY: Logout and a bunch.
Fresh Openbox comes with Restart and Exit items at bottom of the Menu. The first one didn't work for me at all, the second one did (and it means 'logout', by the way). Missing, obviously, are Shutdown (and Suspend + Hibernate, if we talk of laptops).
I installed script called Oblogout, but also, only thing that worked was Logout. Then I copied 'vsido-exit' script from /usr/bin/ of my Vsido install. And it worked like charm. It's not fancy-looking and missing Hibernate, but it's OK with me. Abstractedly, in Xubuntu, you have to have a script that doesn't have bits like 'gdm' and 'hal' in it. 'dbus', of the contrary, is a desirable bit.

That's it. Except strange case of two apps persistently missing few icons, everything is mint for me.