when I weld I will be doing it with Silicone bronze rod and a TIG welder. Tack a ltitle bit, hit it with the blower on the air compressor to cool it off, then tack further down and repeat.
Tack welding rather than a continuous bead keeps heat out of the panel, as does the silicone bronze rod. Moving the tacks around also keeps heat buildup from taking place. The air hose trick is something new a buddy told me about that I haven't tried before but it makes sense.
The other benefit of the silicon bronze rod is it is easy to sand - keeping heat from building up in the panel ones again. Plus it doesn't rust!
If I wasn't cheap I'd get some silicon bronze wire for my MIG and put even less heat in the panel by MIG welding. I think my TIG method will suffice though.