I just wanted to share that ZeroTier is super cool. You just install it and it works automagically. I have pretty much all my networks connected via ZeroTier and I can access them wherever I am and not worry about NAT or dynamic DNS etc etc. It just works!
If you have an OpenWRT device, you could install the ZeroTier client on the router itself and maybe use that as a gateway to avoid having to install the client on other devices on the network. (Just need to adjust the routes accordingly)