take a look at my other designs https://www.thingiverse.com/mg_evolution/designs
I have designed these for my 5mm foam board nutball.
Im using 1806 brushless motors with ESC attached direct to the motor.
(The motors came off a 3" quad)
Im using two motors due to one motor with a 5" prop not having enough power. The benefit if needed is also allowing the motors to help turn the plane if needed.
There is 1 fixing at the rear as the nutball plane slips into the motor mount and is the main support.
This is still a work in progress so parts may change.