I have a NAS box attached to my 2800VG but I do not want any other devices on the network able to see it wired or wireless, however still be able to see this via the Web as I use this was a remote backup.

I have tried it myself without little success can someone advise

On the 2800 you can use the port based VLAN to block access to it - that's under LAN then VLAN, on there make one VLAN with the port that the NAS is plugged into and another VLAN with the rest of the ports.
I'm not sure how you would block it via wireless though, the 2800's WLAN VLAN setup is rather confusing but there should be some stuff on www.draytek.com under support > application notes that would explain it.