Ubuntu Servers :: Remote Backup Ftp Server With Confidential Data?

I already have an ubuntu backup server in my location and need this one server to be backed up remotely in another state. this other location is a helpdesk so there's a danger that they can gain access to confidential data. I'll be setting up this new server as an ftp server but need to set the ftp folder to only allow access to the backup server and me. Because its remote on the helpdesk side, they'll need some access to the file system but need to be completely blocked off from the ftp folder where all the data is at. How can I make sure I can keep them away from my data and still be able to retrieve or copy files over without permission issues between both servers?