I did my commercial in a Piper Arrow and I never once touched the trim. GA aircraft are designed to not require control input to keep the aircraft coordinated during cruise flight. You need right rudder on takeoff and climb, and maybe even a bit of left rudder on descent, but no rudder should be needed during cruise.
That being said, I have flown a couple of beat-up 172s that needed a little rudder pressure in situations that shouldn't have needed it. That's something the mechanics need to fix.
But none of the left-turning tendencies have much effect during unaccelerated, level flight. You usually encounter them in slow, high-AOA, high-power flight, at least in a Piper Arrow. It's not a P-51.
