Would buying CF bonded plywood do the same thing for the rudder tray, just one step?
Carbon Fiber Poplar Plywood Core Sheets
or
Carbon Fiber Herex Foam Core Sheets
or
Carbon Fiber Balsa Plywood Core Sheets
I think these are from PT Model over in Europe

I too have an unopened package of Radio South CA hinges from back in the 80’s
They are still available ...

Pro-Hinges ? radiosouthrc.com