Private Snap Store?

I'm deploying a lot of IoT devices with Core 16 installed on them. The environment that I am installing the devices into does not have direct internet access. I would like to update snaps that we have in our default build.

I can't expose the default snap store to the devices. I can set a server up to act as repo for a snap store, assuming the snap store can be sync'd to a local server. The example of private snap store on snapcraft looks somewhat out of date.

The devices in question have a hardware vendor specific kernel installed. I don't know whether these snaps live in the default snap store or whether they are themselves already in a private or brand snap store. I can't find a setting on the device that gives that away.

Any ideas?