How to merge 4 box colliders into one collider?

Hi everyone!

At the moment i am making a game with a border. I have created 4 box colliders, but was just wondering how
i could mesh these together so i don't have to have 1 script attached to each of the box collider border

 

You can put multiple box colliders on a single object.

 

I have done that, but then the script does not work -

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class WorldBorderScript : MonoBehaviour {
6.  
7.     float borderTimer;
8.     public Transform Player;
9.  
10.  
11.     void OnTriggerEnter(Collider other)
12.     {
13.         borderTimer = 10;
14.     }
15.  
16.     void OnTriggerStay(Collider borderCollider)
17.     {
18.         borderTimer -= Time.deltaTime;
19.  
20.         if (borderTimer <= 0)
21.         Player.transform.position = new Vector3(Random.Range(-40, 40), 0.5f, Random.Range(-40, 40));
22.     }
23. }
24.  

 

The WorldBorder script only works when its on the boxcollider and not on the parent object