Hey all,
Sorry for my VERY late reply. I tried 1001 things to get Rockstor to install, none worked. I finally managed to install it by using a laptop as in-between device. I added the USB drive with Rockstor to the laptop, added the destination drive as well, then booted the laptop from the USB drive and installed Rockstor on the destination drive. I then put the destination drive into the server and managed to get it running that way. A bit of a hassle, but it worked.