vara4,

You will get lots of opinions on this subject, however I am in the opinion that butt welding the panels is the best way to go. The suggestion that was given regarding skipping around is a great one, however I am not known at times for being the most patient. I work for a Company that has GM/Jeep Dealerships, and I go to the body Shop and learn from those guys a lot. They all like to use an Air Gun to cool the weld (for flat rate), and when I have brought it up on Forums, people say it doesn't work-I think it does because the smaller the HAZ (Heat Affected Zone) the less shrinkage you will have, and therefore the least amount of warping. The only thing I see that is a potential downside is that your air had better be dry or you may force water into the joint.

The guys in the Body Shop also love panel bonding, but I think you may get "ghosting" (on a hot day see faint lines in the paint)-they tell me thats the standard in the Industry today, and I'm certain it's as strong or stronger than a weld.

If you really want it nice with minimal distortion, obviously hammer welding is the way to go. And don't for get about the Epoxy Paint inside and out so it won't rust!