Installing Node-red packages that are not in the NPM registry

I am trying to install the Victron package node-red-contrib-victron from ( I have included “npm_packages”: “node-red-contrib-victron”, in my node-red config file however I get:

‘[15:26:01] INFO: Starting installation of custom NPM/Node-RED packages…
npm ERR! code E404
npm ERR! 404 Not Found - GET - Not found
npm ERR! 404
npm ERR! 404 ‘-@latest’ is not in the npm registry.
npm ERR! 404 You should bug the author to publish it (or use the name yourself!)
npm ERR! 404
npm ERR! 404 Note that you can also install from a
npm ERR! 404 tarball, folder, http url, or git url.
npm ERR! A complete log of this run can be found in:
npm ERR! /root/.npm/_logs/2020-02-04T05_26_09_468Z-debug.log
[15:26:09] FATAL: Failed to install a specified npm package’

The package cannot be installed as the package hasn’t been registered in the NPM Registry. The log file suggests that I can install it from either tarball, folder, http url, or git url.

I would really like to know how to install it from either a folder or tarball as I would like to customize it a little to fit my specific requirements. I haven’t been able to find out how to specify a folder or tarball for the “npm packages” in the config file. Any help would be appreciated