go to lowes or home depot by the gutter section. they sell 2 inch thick4 x 8 pieces if styrofoam for about 15 dollars. get 2 side by side and trace the outline of the u with a pencil. remove the u then transfer the line 2 inches smaller all the way around. cut the foam with a hacksaw then mount it to the wall with a little bit of liquid nails. then mount the fathead to the styrofaom and it will look 3d since it will be standing 2 inches off the wall.