butt welding is the way to go i have done body work for 30 years and a good butt weld takes work but when done rigth very litte filler needed .i did a lot of cab corners this way and used very litte filler. a lot less filler that with a over lap. the over lap will takes more heat to weld it.a butt weld will take less and will pull the metal to gether this will keep it from warping in some places . but if you in the middle of a hood or roof you are on your own. and dipping sounds good but i have a customer that had his cab dipped and all seams are rustting nice