Shameless plug - this is exactly the same problem that our team had when we had to maintain a bunch of our customer's servers. All of the subnets were same, and we had to jump through hoops just to access those servers - vpns, port forwarding, dynamic dns with vnc - we've tried it all. That is why we developed https://sshreach.me/ - now it's a click of a button.

The initial idea started as a bunch of ssh tunnels. Been doing that for years. But WireGuard seemed a better solution at scale, and more efficient. When I first saw WiteGuard, it blew my mind how elegantly simple it was. I always hated VPNs. Now I seem to have made them my life...