This is how I set up a Pi Zero W to save DSLstats Snapshots and DataStore to a NAS. It may not be the most elegant solution, but it works for me! I have removed personally identifying info, so you will need to modify where necessary to fit your situation.
Background Info: My NAS has a folder available to all registered users, named "GoFlex Home Public".
1. On the NAS, in "GoFlex Home Public" create a folder named "DSLstats", and within that create two further folders named "DataStore" and Snapshots" respectively.
2. On the Pi create a folder to act as the local mount point for the NAS.
mkdir /home/pi/NAS
3. Create a "Credentials" file
sudo nano /home/pi/.NAScredentials
This file has only two lines:
username=yourusername
password=yourpassword
The items in bold should be changed to the appropriate ones registered on the NAS.
4. Change the file permissions:
sudo chmod 600 /home/pi/.NAScredentials
5. Modify the file /etc/fstab (after making a backup), by appending the following line
//192.168.xxx.xxx/GoFlex\040Home\040Public/DSLstats /home/pi/NAS cifs credentials=/home/pi/.NAScredentials,sec=ntlm,vers=1.0,rw,file_mode=0777,dir_mode=0777
6. Check that the NAS is mounted correctly by fstab
sudo mount -a
7. In DSLstats>Configuration>Snapshots, change the Snapshots directory to /home/pi/NAS
/DSLstats/Snapshots
8.In DSLstats>Configuration>Data Store, change the location of the data store to /home/pi/NAS
/DSLstats/DataStore
9. Reboot the Pi.
I hope this helps.
Edit: Removed wrong part of path in steps 7. & 8.