Creating a box with mylar please help asap

WHEN YOUR MAKING A BOX WITH MYLAR WILL THE INSIDE OF THE MYLAR BALLONS WORK JUST AS WELL.

AND HOW DO YOU HANG THEM IN YOUR BOX CAN TAPE BE USED TO KEEP THE MYLAR UP MY BOX IS TO THICK TO USE PINS.
HELP ASAP THANKS

tape small pieces of cardboard to the mylar and then staple through there. The tape and cardboard take the strain off the mylar and prevent tearing.