[David J]

You overlapping or butt welding ?

If overlapping small sheet metal screws along the edge as needed to keep it tight . Remove them as you go and weld the hole shut .

If butt welding small machine screws-nuts and small washers as needed and again remove as you go and weld hole shut .
This way you actually drill through the seam so half a hole on each panel .
Simpler than it sounds .
Also if butt welding a flat piece of copper behind really makes the weld easier .