There’s a nice little tool for keeping data in sync over various devices, which allows for maximum control and is open source, too: syncthing
Apparently it’s even available for OpenWRT, too: There’s an ARM executable availble on the homepage and an init script that allows for automatic startup in OpenWRT: https://github.com/brglng/syncthing-openwrt
Please include it in Turris firmware 
Hello
It wouldn’t be hard to create it as package. But I don’t think that we should
add packages that are not in OpenWRT and are not part of Turris. Not that we don’t
want, but I think that better way is to create such package in mainstream OpenWRT,
which would propagate to TurrisOS. In meantime Syncthing updates it self, so no
other administrative task is required after deployment.
Anyway please be advised not to use Syncthing on internal storage. It does a lot
of write cycles in its internal database and can wear out flash, which is not
addressed in init script you have linked. Because it’s database and loosing it
means loosing configuration, it is no good to put it to ram. So only other option
is when you use some other storage (that you probably do, where would you put
synchronized data otherwise) and place database there. See ‘-home’ option.