Thanks for the suggestions. I don't have much experience in body work, so much of my thinking comes from reading and I'm sure things will change as I work through the project. I'm glad it'll be quite a while before I need to mount the rear fenders again and don't have to make any final decisions yet. I'm still mulling over what to do with some of the brazed areas of the fenders. The main concern is not the brazing, as much as the general quality of the work. There original fender wasn't trimmed to accept the patch piece, so there is a great place to collect moisture and tattered, rusty metal on the back side. The amount of bondo it took to cover the brazed area was more than I'd like to see on the finished car, but we'll see how I feel when it comes time to deal with it.
I'm using fluid film / lanolin to protect while I work. I feel like it is helpful to be able to see the bare metal. I'm not ready to lay down epoxy primer and I don't want to have to strip off temporary paint layer (even through I will have to clean off the lanolin).
As for weld-through primer, it's my understanding that it is only meant to be used where it'll get heated during the welding or where epoxy primer would burn away - so it can't be painted before welding. So far, my knowledge in this area is just from reading and testing the weld through primer on the bracing and practice welds for impact on the welding.
This is one refence from the
HAMB:
Weld thru primer is used in modern collision repair to replace the zinc coating imbedded in modern sheet metal, only when it is ground off during the repair. It was designed to be used ONLY on bare metal mating flanges. And YES you weld right through it. Absolutely NOT for use on the inside of enclosed panels.
It has very poor adhesion properties. It WILL fail and peel if used on surfaces other than the inside flanges in a pinch weld. It's one of the most misunderstood, and misused products in the industry. Some manufactures do not even allow it in their repair procedures at all.
It works by galvanic corrosion. The zinc or copper corrodes and forms a "seal" against further corrosion, rather than breaking down like steel corrosion. When a plug weld is made on a pinch type flange the primer liquefies and then has some ability to "wick" back in around the weld. It's a "better than nothing" product. The joint still must be sealed completely after welding or it will still corrode. It's just a PART of the corrosion protection process used in modern collision
That said, I use it in both modern collision and restoration, but only where its "pinched"
between two pieces of steel. I prefer the copper from UPOL. I think it has less effect on the weld, than the zink. Tests I've read claim both are about the same in their "limited" corrosion protection.
I look forward to hearing what experiences y'all have had.