SEPM to GUP in semi-isolated network

We use SEPM 11.7 for our main network. We have a sub-network not attached to it. The sub-network has a SEPM server and clients, same version as main network.

We connect the sub-network's second NIC to the main network to go out and get updates once a week. Apparently this is an incredible chore for that server.

My idea and I was wondering if it will work...

Remove SEPM from the sub-network, and set it up as a GUP and the clients will contact the GUP to get updates. When we connect the second NIC on the server, it should pull latest updates from the SEPM server in the main network. Right?

OR

Should we setup the server and clients to connect directly to the SEPM?

OR

Is there a better idea? lol