Patch panel welding - body guys

Mike - I don't recall off the top of my head. My kids gave the 4 piece set to me for Christmas. But my panels are not coated and seem to be hand formed, while the new wheelhouse is stamped and coated.

Oldman - I guess I could do it that way if I did the patch panel 1st and then put the wheelhouse in, but I don't know if I will be able to finagle it in behind the bedside after the fact.

I had figured spraying the inside with weld thru primer or spray cold galvanizing before and after welding the new pieces in, and then rubberized undercoating the best I can. Was also going to flange the original so the seam is upside-down, not allowing wetness to collect in it?