How to show video files via OSMC webserver

Well I used the web interface and reconfigured it to use a different skin (AWXI) than the default.
I also changed the samba domain from workgroup to the one we use here.
I can reach the web interface from my laptop but the only source of “Files” that is available is the NAS located back home (not accessible from this location).
The strange thing is that the locally attached 1TB usb drive named “MEDIADRIVE” on which most of the material resides is not even listed as a file source.
So basically the web interface seems able to go to the VIDEO_NAS source, which is not available on this network, but not to “MEDIADRIVE” which is a physical drive attached to the RPi itself!
Really strange. One would have thought that the most accessible file source would be the local drive…
This OSMC unit has been moved along to the vacation home over the summer and provided with a WiFi dongle for network access over here (Ethernet back home). The VIDEO_NAS resides on the home network (Ethernet) which is not available here.
Any solution for reaching the mediadrive disk content via the web interface?