This happens to be a fuse-block that does have a grounding bus-bar.
However, since your fuse-block does not have a grounding bus-bar, you can install something similar to my old system which I point out towards the end of this video.
I attached a heavy 6 gauge green grounding wire directly to the frame of my trailer by drilling a hole in a non-structural part of the frame. Grind this area to bare metal, apply dielectric grease, and then bolt the grounding wire to this point.
This grounding cable is then run up inside the trailer to a common grounding busbar with multiple attachment points. All your appliances can then be grounded at this one common point.
I also have a separate grounding cable that runs from battery
negative to an attachment point on the frame.
Ignore the references to the shunt and battery
monitor information as this does not apply in your case.
YouTube - Fuseblock Connections_0001.wmv