Here is a exellent script for syncronise your seedbox and NAS.
Step 1 : Login as root and run the following commands
git clone https://github.com/4r3/synchro-seedbox
chmod +x makeinstall.sh
Once you run it you will get the below question , It is in French so you might have to use a bit of google translate to make sense of it .
Rest should work out fine 🙂
Thats pretty much it once you have set everything up you will have a runnign sync between your seedbox and NAS.
If you want to sync more users you have to just run the script again.Which would look something like this, remember to login as root in your seedbox server.
and then follow through the instructions again.
You can also save it as a script if you do it often.
Hope that helps you and special thanks to the guy who made it and here is the github link : https://github.com/4r3/synchro-seedbox