Instantiating objects randomly based on the length of an object

Searched everywhere and tried various ways but I don't believe I am able to do this. I want to make a group of 3 asteroids (that are randomly selected) spawn based on the length of an empty gameobject (I am using box collider to determine length). I currently have it based on random z or x axis but those are creating some wonky things and making it so its based on the length of a particular axis of a collider sounds much easier and more automated.

The setup I have now is an empty gameobject called "Asteroid Generator" and a child (that has this script and does the spawning) called "Asteroid Spawner"

I also plan to have another child within generator that will be the same box size that will end up deleting all asteroids that pass as well as a timer that will randomly spawn the asteroids rather than spawn infinite asteroids at once.

Here's what I have:

 #pragma strict
 
 var asteroids = new GameObject[3];
 var pos1: float;
 var pos2: float;
 
 
 
 function Start () {
 }
 
 function Update () {
 //    for (var child : Transform in transform) {
         for(var i : int = 0; i < asteroids.length; i++)
         {
             var randomPosition = Vector3(transform.position.x, 0, Random.Range(pos1, pos2)); //randomly spawns asteroids across z axis (done here as forloops update here)
             var thingToSpawn : int = Random.Range( 0, asteroids.length ); //chooses randomly diferrent asteroids
             var setAsteroid = Instantiate( asteroids[thingToSpawn], randomPosition, transform.rotation ); //instantiates selected asteroid 
             
             setAsteroid.transform.parent = transform;
             Debug.Log("instatiating");
         }
 //    }
 }