How do you configure your custom portable shelf set/tab?

[AdamM]

I'm trying to move a bunch of my custom tab tools to my own .shelf file that exists outside of the houdini installation areas.
This should hopefully make setup on new machines/versions of Houdini much easier.

I have saved a adam.shelf file in C:/outside/toolbar

I've tried a few approaches to get Houdini to read these shelves on startup.
Firstly I added the following to

houdini.env

HOUDINI_TOOLBAR_PATH = $HH/toolbar;C:/outside/toolbar

Although this works, it caused the SideFXLabs toolbar to not register (the shelf was there but the tool buttons had disappeared)
I guess I'm removing the SideFXLabs toolbar path with the above entry??

So the next approach is to append the paths in 123.py, however the existing value of HOUDINI_TOOLBAR_PATH is None!
Anyway I add all the paths and try to hard code the SideFXLab path (I DONT LIKE DOING THIS).

In 123.py 

# ADD CUSTOM SHELVES FROM _houdini_
shelf_paths = [
    "$HH/toolbar",  # existing path is always NONE!?
    "C:/Users/me/Documents/houdini19.0/SideFXLabs/19.0.657/SideFXLabs19.0/toolbar",  # existing path is NONE!?
    "C:/outside/toolbar"
]
existing_shelf_path = hou.getenv("HOUDINI_TOOLBAR_PATH")
print("Existing HOUDINI_TOOLBAR_PATH: ", existing_shelf_path)
if existing_shelf_path is not None:
    shelf_paths.append(existing_shelf_path)

shelf_string = ';'.join(shelf_paths)
print("shelf_string: ", shelf_string)
hou.putenv("HOUDINI_TOOLBAR_PATH", shelf_string)

The result was the same,
All default toolbars and My toolbar work, but the SideFXLabs toolbar does not 

Is there a better approach to keeping my tools separate from the default.shelf ??
Particularly keeping them in an outside directory, so that all my custom stuff is more portable?

Thanks.

[AdamM]

As usual, I search for hours and find nothing. 
Then just after posting I find this

 

TLDR for future visitors
add a ";&" to the end of your env vars or it will not append the existing ones.