I used what is called the backing strip method. You can see it explained here:

http://www.autobodystore.com/door_rust.shtml

Benefits are that you get the strength of a lap without the problems that come with trying to flange a curved piece of metal like we find on these trucks. I used seam sealer on the backing strip after all was welded in to seal it up from moisture.
Regards,
Steve
New Orleans