Perform image push over public IP network

Hello,

our scenario involves several 5010 (D90D8) WES8 devices that are located at several different locations. We have a central WDM (5.7.2) server that is accessible (although firewalled) to the Thin Clients through FTP over a public IP network. Up until now we have been able to deploy individual small RSP packages successfully using WDM. However, now we would like to push a full new system image using this same route.

Is this possible, and what prerequisites do we need to meet? We have access to all relevant firewalls should we need to make any modifications.

We performed a short "get device image" test but this failed because Merlin probably wasn't able to determine or contact the WDM server. Possibly because the WDM is not on the same local network?

Thanks for any help, regards