Butt Welding 18 Gage w/MIG?

Can anyone point me to a tech article on welding patch panels?

I'm replacing some floor pan sections in a '65 Dart and I need to make the butt welded seams look good from both sides. So far, it's not going too well :confused:

I'm considering using the copper plate backup method to try and get a better result. Comments, pictures, tutorials, help!

Thank you... dartlover