@Sieggie or anyone else having a problem with the Prince either bouncing around or just an immediate "overstressed" condition, I have finally found a fix for it. Maybe a bit Mickey Mouse, but I used the aircraft.cfg from the Hunting Percival Pembroke with a few changes to it and it now flies as expected. I haven't heard anything regarding my email to Rob. He may be on holiday or just not responding to emails.
When you said you replaced the aircraft.cfg file I looked to see what in the file could cause an over-stress. I found these were all set to zero so any stress would cause the air frame to collapse. I just picked some larger values but if you look around at similar aircraft you can most likely get better numbers.
[airplane_geometry]
positive_g_limit_flaps_up=4.000000
positive_g_limit_flaps_down=2.000000
negative_g_limit_flaps_up=1.500000
negative_g_limit_flaps_down=1.500000
Dave