I like to use a flanged seam, hammer welded all the way to keep things smooth and the seam tight. There is no quick way to do it....used to be a product called Moistbestos that you could use to soak up the heat, but the feds took that away. Bonding panels is probably fine if you're in a body shop working flat rate. I've yet to see a glued panel that doesn't ghost out a seam line after a few years. Think I'll stick to welding mine! Usually I use the Mig for the tacks then the Tig to fill in the blanks, but using a Mig for the whole process is just fine, too.

When I have a long weld to do joining a couple pieces together, I try to make that the secondary job for the day and spend the cooling time for the welds working on something else.