Another antenna question

Still looking for an external antenna for my handheld. I am now thinking
about putting it on the back side of the baggage compartment inside of the
fuselage. This is in a wood and fabric airplane. The back of the
compartment is approximately 8"x24" made out of 1/8" plywood. What I would
like to do is use a piece of sheet aluminum (8"x24") on the back inside of
the baggage compartment for the ground plane and putting the comm antenna
inside the fuselage behind the baggage compartment. The antenna I would
need to use would be one with the 45 degree bend in it.
Is this a big enough ground plane? If not could I bend the sheet at 90
degrees and extend the aluminum out horizontally to get more area. Also
does
it matter if the antenna is in the middle of the ground plane.
Thanks
Dave