Keeping the camera in bounds

I have a 2D Orthographic camera. Its pointing at my background GameObject. The background has a Mesh and a MeshRenderer on it, its created by UniTMX. I would like to let the player drag the camera around but I want it to always have the background visible and covering the full screen.

This is what I'm trying... Its not really working at all. I'm guessing GameObject.Find("Background").GetComponent().sharedMesh.bounds isn;t what I should be looking at.

 using UnityEngine;
 using System.Collections;
 
 public class CameraController : MonoBehaviour {
 
   enum Mode {Idle, Follow, Drag}
 
   private Bounds backgroundBounds;
   private float rightBound;
   private float leftBound;
   private float topBound;
   private float bottomBound;
   
   private Mode state = Mode.Idle;
 
   public Transform followTarget;
   private Vector3 pos;
 
   public float dragSpeed = 2;
   private Vector3 dragOrigin;
    
   void Start () 
   {
     float vertExtent = Camera.main.camera.orthographicSize;  
     float horzExtent = vertExtent * Screen.width / Screen.height;
  
     backgroundBounds = GameObject.Find("Background").GetComponent<MeshFilter>().sharedMesh.bounds;
     leftBound = (float)(horzExtent - backgroundBounds.size.x / 2.0f);
     rightBound = (float)(backgroundBounds.size.x / 2.0f - horzExtent);
     bottomBound = (float)(vertExtent - backgroundBounds.size.y / 2.0f);
     topBound = (float)(backgroundBounds.size.y  / 2.0f - vertExtent);
 
     Debug.Log(backgroundBounds);
   }
    
   void Update () 
   {
 
     // Switch Modes
     if (Input.GetMouseButtonDown(0)) {
       state = Mode.Drag;
       dragOrigin = Input.mousePosition;
       followTarget = null;
     }
     else if (!Input.GetMouseButton(0) && state == Mode.Drag) {
       state = Mode.Idle;
     }
     else if (followTarget && state == Mode.Idle) {
       state = Mode.Follow;
     }
 
     // Drag camera around
     if (state == Mode.Drag) {
       Vector3 mousePos = Camera.main.ScreenToViewportPoint(Input.mousePosition - dragOrigin);
       Vector3 move = new Vector3(mousePos.x * dragSpeed, mousePos.y * dragSpeed, 0);
       transform.Translate(move, Space.World); 
     }
 
     // If we have a target to follow move to them, but stay on the background
     else if (state == Mode.Follow) { 
       var pos = new Vector3(followTarget.position.x, followTarget.position.y, followTarget.position.z);
       transform.position = pos;
     }
   }
 
   void LateUpdate () {
     Vector3 v3 = transform.position;
     v3.x = Mathf.Clamp(v3.x, leftBound, rightBound);
     v3.y = Mathf.Clamp(v3.y, bottomBound, topBound);
     transform.position = v3;
   }
    
   void OnLevelWasLoaded ()
   {
     Start();
   }
 }