Since Panny has been out of the Car Stereo business for a while now...there is probably no help available on that front. My own experience with such codes is that the mfr. dealer/installers used to be able to crack the code with some sort of factory reset...but that bit of knowledge is probably long gone.
Another possibility is that the Coach mfr. set all the radios with the same security code...doubtful that they went to this trouble....but worth a call.
Finally...there is the possibility that NO ONE ever set the code as it is not required for operation. This might be viewable via menu prompts...if it ASKS you to input a new code...then you probably have nothing to worry about.
The last thing I would say is that your radio as a negative wire black....and two power wires red and yellow (yellow one for memory). Yellow may be wired to the battery directly for constant power... red probably goes to a switch or ignition acc.
The security function is engaged when it LOSES power so that is PROBABLY tied to the yellow wire and black. It should be a simple matter to attach 3 "jumper" wires to a separate 12V battery to avoid interrupting the power supply...then reverse the process when the new installation is complete.
Hope it works out.
Sounds like you have the manual but if not...it is online here:
Operating Manuals for Panasonic Products