I just finished welding up the first of 2 rear door handles on my '63 wagon. I took my time with the measurement, trimming, and welding, and came up with a warp-free panel. I thought to myself, "this welding thing is easy". 
HOWEVER...
After grinding, I had some warpage that approached 3/16" deep in some areas! It took me longer to get the panel semi-straight again than it did to weld it. I thought I was careful to grind in alternate areas, doing small parts at a time, allowing to cool etc - but my process didn't work.
I've got another side to do. PLEASE can someone suggest a process to prevent me from duplicating this mistake?

HOWEVER...
After grinding, I had some warpage that approached 3/16" deep in some areas! It took me longer to get the panel semi-straight again than it did to weld it. I thought I was careful to grind in alternate areas, doing small parts at a time, allowing to cool etc - but my process didn't work.
I've got another side to do. PLEASE can someone suggest a process to prevent me from duplicating this mistake?