correct way to implement cache as bitmap to deeply nested movieclips? help!

I've been really stuck at this problem for a number of days and cant find any help online as to where im going wrong.

the setup as of now, there are 4 movieclips i want to cacheasbitmap. two copies of a vector movieclip called CloudS2 and two copies of one called CloudS4

those are in a movieclip holding them called CloudsNear and another movieclip holding that which holds an animation of the CloudsNear movieclip moving past the screen in a loop which is called CloudsNAnim

and that is inside the main level which is added to the stage called PlaneLevel

where do i place the cacheasbitmap lines in my code to load them into memory before I load the main movieclips

package

{

      // all my imports etc //

    public class MightyMend extends MovieClip

        {

        public function MightyMend()

            {

            // constructor code

            addChild(PLoading);                      //this loads my loading screen png to the stage

            stage.addEventListener(Event.ENTER_FRAME, loading); //reoccuring event listener happens as often as is set by FPS

            PlaneLevel.CloudsNAnim.CloudsNear.CloudS2.cacheAsBitmap = true;    

            PlaneLevel.CloudsNAnim.CloudsNear.CloudS4.cacheAsBitmap = true;     //these lines dont work

            }

        private var PLoading:Bitmap = new Bitmap (new PlaneLoading());       

        private var PLevel:PlaneLevel = new PlaneLevel();   

        public function loading(e:Event):void //

            {

            var total:Number = this.stage.loaderInfo.bytesTotal;

            var loaded:Number = this.stage.loaderInfo.bytesLoaded;

            var percent:Number = loaded/total * 100;

            trace (percent);

            if (total == loaded) //checks if all bytes for all movieclips have been loaded

                {

                stage.removeEventListener(Event.ENTER_FRAME, loading);

                onComplete();

                }

                 //the rest of the code staes that when oncomplete it will remove the loading screen and add the plevel to the stage etc..