Simple and Quick Fix PickUp script

Guys, I am having an issue with a simple script. To make it quick, I have this script attached to my player. I have a couple spheres tagged coin. I collect them and it adds points to the score and destroys the sphere. That part is fine.

Recently I decided I did not want the sphere to destroy. I now wanted it to be spawned to a holding place for the spheres(Coins) in the level. So, I created an empty GameObject and used it as my spawn point. So now when I collect the coins, they all go to that location. Fine.

The problem is that I want them to collect inside the holding area realistically. Imagine a glass and you you drop marbles in it. So I set the spawn point above the container and added a rigid body to the spheres. The spheres now automatically fall through the plane. I tried making the colliders all primitive and tried making the plane a mesh collider and the spheres primitive but its a no go. They just fall through the floor. Where am I going wrong. And also is it possible that some one can give me hints as to the best way to approach using an array to keep track of the amount of spheres in the container? something like the container has 5 boxes then I can no longer collect any boxes.

     var score = 0;
 var scoreText = "Score: 0";
 var track : AudioClip;
  
 var packTruck : Transform;
  
 function OnTriggerEnter( other : Collider ) {
     Debug.Log("OnTriggerEnter() was called");
     if (other.tag == "Coin") {
         Debug.Log("Other object is a coin");
         score += 5;
         scoreText = "Score: " + score;
         Debug.Log("Score is now " + score);
         audio.Play();
         other.transform.position=packTruck.transform.position;
     }
 }
  
 function OnGUI () {
      GUI.Label (Rect (10, 10, 100, 20), scoreText);