Help to backup using rsync to Asus router (RT-RT66U) running Merlin

[wde]

I'd like to do a two-way sync between my NAS (AS-602T) and my router (RT-AC66U running Merlin firmware 380.58.alpha3).

I have managed (through the nice easy way) to install entware on an HD attached to the router.
I then installed rsync and rsyncd from entware - seems good so far.

I need help in knowing which/where files/scripts/other are needed to be modified/created on router to get rsycn to work with backup module on Asustor AS-602T.
I have a very limited knowledge of linux but have become familiar with PuTTY and WinSCP.
I've found several examples on the web, but all are a little different and confusing (to me).

Any help would be appreciated.