Panel mount DC connector
What I would do in your case is mount the panel connector (last picture) in your case. Then solder wires to that connector (it is indeed ment for soldering wires, not for PCB mount) and solder the plug to the other end of the wires. Then you can use the connector that is already on the PCB to connect the plug internally. 



Other option would be to solder the wires from the panel mount connector directly to the PCB.