The splice plate is formed from a short section of the aluminum trim coil, scored and snapped off the roll. Here it is taped to the insulation to support it while applying adhesive.

I used 3M Super 77 contact cement. The right side of the splice plate and the backdrop was later masked off, then adhesive was sprayed on the back of the backdrop and the left side of the splice plate. Both were allowed to get tacky, the the backdrop was pressed onto the splice plate, with the insulation providing support. You get one try.

Later a similar process was repeated to join the next section of backdrop to the exposed side of the splice plate.