Please help me convert this script from using position to rotation?

Hi. I am working on a script that gives my FPS weapon a more realistic 'sway' effect:

In this script I have used the mouse input and localPosition to create the effect...

 var speed : float = 1;
 var maxAmount : float = 1;
 private var newPos : Vector3;
 private var localPos : Vector3; 
 private var movementX : float;
 private var movementY : float;


 function Start(){
 localPos = transform.localPosition; 
 }

 function Update (){ 
 movementX = Input.GetAxis("Mouse X") * Time.deltaTime * maxAmount;
 movementY = Input.GetAxis("Mouse Y") * Time.deltaTime * maxAmount;
 
 newPos.x = localPos.x - movementX;
 newPos.y = localPos.y - movementY;
 newPos.z = localPos.z;
 
 transform.localPosition = Vector3.Lerp(transform.localPosition,newPos,speed*Time.deltaTime);
 }

I have decided that changing the position of the object isn't the right way to create a realistic effect. I have tried to use localRotation and Quaternion like this...

 var speed : float = 1;
 var maxAmount : float = 1;
 private var newRot : Quaternion;
 private var localRot : Quaternion; 
 private var movementX : float;
 private var movementY : float;
 
 
 function Start(){
 localRot = transform.localRotation; 
 }
 
 function Update (){ 
 movementX = Input.GetAxis("Mouse X") * Time.deltaTime * maxAmount;
 movementY = Input.GetAxis("Mouse Y") * Time.deltaTime * maxAmount;
 
 newRot.x = localRot.x - movementX;
 newRot.y = localRot.y - movementY;
 newRot.z = localRot.z;
 
 transform.localRotation = Quaternion.Lerp(transform.localRotation,newRot,speed*Time.deltaTime);
 }

This script doesn't have any effect of the weapon, it just stays 'static', even if I crank the speed up to 999. So can someone please help me with this problem? - Thanks