Phone home VPN (MSP Management)

So I am currently working for an MSP that uses mikrotik at a lot of our voice or internet only clients. We currently have a few deployed mikrotik's that are behind a NAT (roughly 50). We probably have a good 200 others that are public facing. Since we need a tunnel to manage the 50, I am trying to find a solution to setup a "phone home" VPN for management only of all the routers so there is a standard. I currently have an SSTP VPN setup on all the ones that are not remotely accessible, but I was hoping to find something that I could make a standard across all sites, quickly and efficiently. My other problem is making them unique will take quite a bit of time (250+ VPNs). Anyone have any experience with this? Other people have a use case where if I started working on a public coding they could contribute or utilize?