Customs bonding dissimilar materials

So I have a roof that the front is steel, but the rear is aluminum. I can use the existing wood roof rails to tack the two pieces in place permanently, but am looking for suggestions on covering the seam this would create. Fibergl***? Bondo? Some sort of Targa strap thing?
Concerned about the seam showing up later, thru the black paint.

 

SEM general purpose panel bond works great in those situations