Apply Texture from AssetBundle

I want to store the Textures (and Sprites) in my project externally then apply them when the Apps running. I tested with downloading each from a URL and applying them and that worked in a simple capacity but it was too much for the device when I tried to load all the Textures from their own unique URL.

So I thought the next logical step would be to bundle them together load them from an AssetBundle. So I exported my bundle of Textures then applied the following script to each object that requires a Texture. The url is my Desktop (where the AssetBundle sits) and the assetName is assigned in the Inspector (as each is different):

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 using System.IO;
 
 public class LoadTex : MonoBehaviour {
 
     private string url = "MY_DESKTOP_URL";
     public string assetName;
 
     IEnumerator Start()
     {
     WWW www = new WWW(url);
         yield return (www);
         AssetBundle assetBundle = www.assetBundle;
         Texture tex = assetBundle.LoadAsset <Texture>(assetName);
         Renderer renderer = GetComponent<Renderer> ();
         renderer.material.mainTexture = tex;
     }
 }

I don't get an error message in the Editor, but when I go into Play Mode I get the following errors:

     You are trying to load data from a www stream which had the following error when downloading.
     Error
     UnityEngine.WWW:get_assetBundle()
     <Start>c__Iterator0:MoveNext() (at Assets/Scripts/LoadTex.cs:18)
     UnityEngine.SetupCoroutine:InvokeMoveNext(IEnumerator, IntPtr)
     
     NullReferenceException: Object reference not set to an instance of an object
     LoadTex+<Start>c__Iterator0.MoveNext () (at Assets/Scripts/LoadTex.cs:22)
     UnityEngine.SetupCoroutine.InvokeMoveNext (IEnumerator enumerator, IntPtr returnValueAddress) (at /Users/builduser/buildslave/unity/build/Runtime/Export/Coroutines.cs:17)

Can anyone help me out with this?