Our three identical pieces are stacked up and glued together. To glue them I use our "Base Paste" adhesive. White glue or any type of styrofoam glue will also work. Since we will need Base Paste later in this project, we can save some money by using it in this step as well. If you want to secure the pieces together while the glue dries, push some long nails into the foam.
Take another piece of styrofoam and cut out a lid or top for your tunnel. Since we will shape these pieces to fit later, you don't have to be to fussy about exact fit now.