How to ensure that an object always rotates toward the camera?

I'm trying to make a program that lets its user rotate a model horizontally and vertically to look at different parts of it. I have horizontal rotation all set up, but vertical rotation is proving difficult. I want the user to, no matter how they've rotated the model horizontally, be able to tilt the model toward and away from them, with a 20 degree limit so they cant flip it all the way upside down.

Simple rotation on either the X or Z axis makes it so that when you rotate horizontally another 90 degrees, youll be seeing a sideways version of the model.

How do I set the object up to rotate in relation to the main camera while the user holds down the up and down arrow keys?

This is my current script:

 public float horizSpeed;
 public float vertiSpeed;
 public CharacterController cc;
 
 public GameObject artiSphere;

 void Start()
 {
     cc = GetComponent<CharacterController>();
 }

 void Update()
 {
     //horizontal rotation
     cc.transform.Rotate (new Vector3(0.0f, Input.GetAxis ("Horizontal")*horizSpeed*Time.deltaTime,0.0f));
 }