I started with a really thin piece that easily bent to the contour of the shield and glued it to the backside (sorry no pic). Then using two thick pieces (about 3/32") I pinned them together in the middle and glued them to the thin sheet and the edge of the shield. I also had to add a couple thin layers at the bottom of the shield (not shown in pic) to make up the difference in depth.
I then sketched out the shape of my shield and used my dremel to trim and sand it to shape.
Finally, added some putty to fill in any gaps. Let it dry and then sanded it all smooth.