Applying a script to multiple gui boxes

Hi, I have written the following script that draws a gui box then allows the user to drag it around the screen. However, I need to be able to add boxes dynamically and be able to drag them all. How would I modify my script to be able to accommodate for multiple boxes?

    private var progress: int;
    var mySpeed: int;
    var pos: Vector2; //position of box
    var size: Vector2; // size of box
    var within: boolean = false; //checks if clicked inside box
    var mousePos: Vector2; // current mouse positon
    var xOffset = 0; //used to calculate where in the box user clicked
    var yOffset = 0; //used to calculate where in the box user clicked
 
    function OnGUI() {
        // Constrain all drawing to be within a pixel area .
        GUI.BeginGroup(new Rect(pos.x, pos.y, size.x, size.y));
 
 
        GUI.Box(Rect(0, 0, size.x, size.y), "Hi"); //draw the box everyframe
 
        // Always match BeginGroup calls with an EndGroup call
        GUI.EndGroup();
    }
 
    function Update() { //within every frame
 
        if (Input.GetMouseButtonDown(0)) //if user presses the left mouse
 
        {
            mousePos = Input.mousePosition; //get current position of mouse
            mousePos.y = Screen.height - mousePos.y; //used to invert the y value of mousePosition
            if (mousePos.x > pos.x && mousePos.x < (pos.x + size.x)) //if user has clicked with the box's X co-ords
            {
                if (mousePos.y > pos.y && mousePos.y < (pos.y + size.y)) //if user has clicked with the box's Y co-ords
                {
                    within = true; //set within to true to let the script know
                    xOffset = mousePos.x - pos.x; //set where in teh box the user has clicked
                    yOffset = mousePos.y - pos.y; //set where in teh box the user has clicked
                }
            }
        }
 
 
 
        if (Input.GetMouseButton(0)) //if left mouse button is held down
 
        {
 
            if (within == true) //and user has clicked within the box
            {
                mousePos = Input.mousePosition; //get mouse position
                mousePos.y = Screen.height - mousePos.y; //invert the Y coords
 
 
                pos.x = mousePos.x - xOffset; // move the box with the mouse
                pos.y = mousePos.y - yOffset; // move the box with the mouse
            }
 
        }
 
 
        if (Input.GetMouseButtonUp(0)) //if user releases the mouse button
 
        {
            within = false; //set within to false to confirm the user is not clicking anymore
 
        }
    }