Best way to install from a stand-alone network

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I've been having issues installing electric on systems that are deployed to a network that does not have any internet access. I've had limited success using rosinstall on a system that does have internet access to checkout the full install, installing rosinstall on the machines behind the network and then coming up with a custom rosinstall file pointing to both the ros and stacks directories.

However this build does not always work. Just wondering if there's an easy way that given I have all the source code, how do I build the ros core system manually? I managed to get the environment variables setup and build rospack, but couldn't proceed from there.