Crashplan on Duo/NV+ v2? [SOLVED + TUTORIAL]

OK I have made some progress. After a lot of googling and interpretation of the results, I managed to tweak my router to allow me to get all the PCs on the LOCAL network to backup to the ReadyNAS Crashplan server and this has been running smoothly for a week or so. However I also want laptops to be able to back up when they are away from the local network and this is still causing problems.

What I notice is that when I login to the CP server on the NAS and look at the Settings, Network tab it reports the Internal address as 0.0.0.0 and the External address as 81.134.96.126. The actual external address is dynamic and changes every time the router reboots.

I use DynSite to update dyn.com for remote access and this works perfectly from one of the computers.

The actual External address is currently 81.130.76.197 and this is reported by Crashplan on the computers but even after rebooting the NAS unit and restarting CrashPlan the NAS version continues to report 81.134.96.126.

Does anyone know why CP on the NAS is seeing the wrong external address when CP on all the PCs are seeing the correct one?

Thanks