Joe,
You have several options depending on the construction
of your aircraft and how much 'trouble' you want to go to.
A simple 1/4 wave element mounted to a metal structural
member of the aircraft should beat the rubber-duck to
within an inch of it's life (only added weight would be the
antenna element and feed line, no 'plate').
The 'best' place to mount an antenna on an aircraft is
also the least convenient, usually. Guess that depends on
where the motor is (motors = RF noise makers). The center
of the aircraft is probably the 'best' mounting place since
it would give you a more or less omnidirectional radiation
pattern. Directional radiation patterns are NOT desirable
on an aircraft (com or nav)!
Good luck, and let us know what happens...
'Doc