DetMatt is "spot" on. Weld thru primer is very important unless you want to go through this again in the future. Work out from the floor pan and make sure that everything is centered. If you can mark it, remove it, mock it back up and everything looks good, drop your mask and hit the trigger. I measured and mocked up things many times over just to be sure it was correct. Hitting the weld trigger was always a tense moment even when you know you've got it right. Good luck on your project!