I'm going to try this with one of my sample pieces: Cut back one aluminum skin and the plastic middle about 3/4-1" along the edge, lay in a stiff piece of aluminum wire I have, and wrap the other skin over so it laps 1/3" or so on the other side. Epoxy or solder the seam.
Drill the holes for the fasteners and dimple them so the bolt-heads are recessed.
What could possibly go wrong?