npm pack won't install the dependencies. it is useful for installing a plugin in development: npm pack produces a .tar.gz for the plugin's own code. then you can copy that over to the target system, but installing from that file you still need net access for any dependencies.
For this case you need to explicitly npm install all the plugins in an empty directory, using the SAME node.js and processor architecture as your target system [*]. Then copy the resulting node_modules directory under your target system sk settings directory, usually $HOME/.signalk/node_modules
haven't done this, so not sure if there's something i am overlooking
* required if there are any plugins that have native bindings = are not 100% JavaScript