Appreciate the thoughts Bartamos & Kevin. I thought I was just doing something completely wrong but glad to hear that the thin metal can cause problems for anyone.
I will save this thread for reference purposes.
Here are a couple of thoughts of an amateur:
1) I have always strived to just cut out the bare minimum from the rusted area, with the goal of "preserving" more original truck, but now I'm thinking to use more or all of the patch panel to get as far away from rust and into solid metal as possible. Necessary.
2) Try to avoid welding across a fold or bend. This caused problems in the side footwell I was working on. So with my new patch panel the joint will be above the folds or bends in the "flat". I found that the metal in the bend is super thin and I burned thru no matter what. Also when grinding, it is hard not to make the bend thinner than the flat places.
Thanks again for the advice.
Your thinking process and efforts are spot on. With thin metal, careful grinding is as important as careful welding. Many times I weld both sides of a butt joint. I don't grind the unseen side (maybe just grind the tips/ridges down). I tack the seen side, then weld the unseen, then finish the seen side. Then grind the seen with a die grinder. Lowering it's RPM's as I get down near flat.
