I know I'll get a laugh at this but the absolute fix for your problem is
JB-WELD! I have used it on many motorcycle frames to give that smooth look and NEVER had one fail. I was very skeptical when my powder coater told me to do it. I have never seen one crack either (unless it was wrecked)!!
I am getting mine painted next week. Did you get yours done?
Yeah I did! Got a matte textured black finish and I'm very happy with it. I'll post pics this weekend. The powder coat went on thick enough that it covered the seam perfectly without any type of silicone pre seal