Yes, welding will cause ripples in the sheet metal, it seems like they are giving you the straight story. Welding on sheet metal body panels can be a real art to get it right. Low heat is the first thing, tig is probably the best, but mig works good too, I wouldn't try it another way. You have to stich weld it, meaning you make a bunch short small welds along the whole joint so you don't over heat the metal anymore than you have to. Then you go back and keep doing this a little at a time 'till the whole seem is welded. Then grind them down, again trying not to overheat the metal - then you will still have to work the whole thing over with hammer and dollies, then you'll probably still need some Bondo - keep the bondo as thin as possible say no more than a 1/8" - it's a lot of work, and takes a lot of time -
Camo-Ram is one of the real pro welders that I know of on this site, maybe he will see this and have some better tips for you
Camo-Ram is one of the real pro welders that I know of on this site, maybe he will see this and have some better tips for you