Just had an interesting conversation with a POR-15 tech rep.

Here was my thinking, and he confirmed this should work:

1. Clear out the rust
2. Sand the surface
3. Paint raw metal with Rust Bullet (I like Rust Bullet over POR-15 paint in this case because RB is a converter, not just a protective layer)
4. Cover and fill with with POR-15 Epoxy Putty*
5. Sand the putty to conform with the door shell and paint with epoxy primer, on which the base/clear will eventually go.

*Step 4 was the big question mark: POR-15 states you can paint over their putty, but will their putty bond to rust reformer like Rust Bullet? He said yes and that it shouldn't be a concern so long as the surface is sanded.

I'm going to go this route - like I said, worst case scenario this eventually fails and I'll have to replace the door or have a pro cut and weld that area.

Only bad news is I probably won't know how well it will work for a long time!

 

From RB's site:

Is Rust Bullet Compatible with Automotive Fillers, Fiberglass, and Primers?

Body fillers, premium automotive primers, and automotive paint may be applied over Rust Bullet. To insure proper adhesion, Rust Bullet should be sanded with a 100-150 grit sand paper before applying body fillers, fiberglass or premium primers. When working on body parts, Rust Bullet should be layered, i.e. apply two or three coats of Rust Bullet, apply the bondo or fiberglass, and then apply another coat of Rust Bullet. This will seal out any moisture the body filler might attract while adding strength and durability to any weak places. You can apply Rust Bullet over existing bondo, fiberglass, or paint if there is no rust present after scuffing the surface with 100 or 150 grit sand paper or sanding block. If bondo is applied directly to a rusted area it has a tendency to absorb moisture which will cause further rusting and bubbling in the bondo. Rust Bullet works best when it is in direct contact with the metal. The final coat of Rust Bullet should be wet sanded before the application of a top coat.

 

Also just spoke to a Rust Bullet tech rep. She confirmed it will lay fine underneath the epoxy putty and putty should stick to the RB.

She recommended RB Automotive (so not their white/black shell lines...those would work too, but not quite as well). She recommends allowing the RB to fully cure (72 hours is max cure time), and then sand with 80 grit before applying the POR-15 epoxy putty.

 

Update and Question Request.

Update: The POR-15 rust dissolver did its job, no surprises. Solid metal all around, very minor pitting in the worst spots. An ideal candidate for my proposed method of Rust Bullet + POR-15 Epoxy Putty. Lucky me.

Question/request: does anyone have photos of a bare metal XJS? I've done some google searches and the only images I found were pretty poor quality.

Just curious to see what it would look like...as I've taken a few areas down to bare metal, I've thought more than a couple times that it might actually look really cool, kind of like the airplanes and racecars of old. Not a mirror chrome finish, mind you, but like brushed aluminum. They make wraps with this design but I doubt it looks like the real thing. The real trick of course would be protecting it...they do make clear epoxy primers for boats that bonds to metal, but I don't know what "clear" constitutes. Shiny is no good.

 

Forgot to add a pic post-clean. Really was quite minor. Rust bullet should arrive tomorrow so that will be next.