Almost no rudder needed if doing maximum aileron throw rolls with a trainer. They don't do the best axial rolls no matter what you try.

Differential aileron throw helps the roll be more axial. Mechanically adjust the linkages to give up to double the upwad deflection as downward. (its just a matter of using a 6 arm "wheel" and using 2 arms that are NOT directly across or next to each other... for the torque rod typical of trainers... you have the arms forward of center at neutral. This gives more push than pull.

Most trainers... its full ailern and shve the stick full forward (down elevator) just as its ALMOST inverted then back to neutral elevator before its 45Deg banked from nverted headed toward upright. There's still a "wiggle" in the roll... but thats about as good as it get with a trainer.