My opinion of weld thru primer used on our trucks isn't going to prevent rust from forming in the area of the welds. While it is conducive to welding (no contamination), it is destroyed near the welds, providing no rust prevention there. Since the locations we are welding are often multiple spot welds, 3/4" apart, that leaves a lot of bare metal exposed underneath. I don't sweat it much because I use epoxy primer after the body work and that should help keep the rust at bay for a good long time.
Carl
