I would suggest cleaning it with just plain old mineral spirits, then rinse with a jug of rubbing alcohol. I would scuff it with 400 grit paper afterwards. After that, you could spray the inside with a self-etching primer and spray the edges with weld-through primer. There is a way to spray the insides with a rust-proofer after they are installed by using a spray tube through the holes. You can brush the primer, that is fine. As for the dog legs, prime EVERYTHING that you can. Paint it if possible with some rattle can paint as well.

 

The weld thru primer on the inner and outer rocker edges will be fine. You can also epoxy prime these edges along with the inside of the rockers and when the epoxy primer is dry, you can grind away the primer where you will be making your plug welds. I took a piece of thin cardboard and cut a 3/4" circle in it to use as spray painting mask. I held this mask over the area where the primer was ground away and sprayed weld thru primer on those spots. This way gives the areas that aren't being welded the protection of the epoxy primer and the welded areas will also be protected by the weld thru primer. Just remember to scrape away the weld thru primer through the plug weld holes before you weld. Use a scribe or a small screw driver with the blade filed to a sharp edge to remove the primer, welding is easier and cleaner when you start on bare metal.

The inner rocker can be removed from the rear brace without taking the quarter off. You will have to drill out the spot welds from underneath the car that hold the inner rocker to the brace. You may have to use an angle drill for this. Clean off any dirt or undercoating on the flanges of the brace, take some sandpaper and lightly sand the vertical and lower flanges. This will help you see where the spot welds are, they can be hard to locate. There should be two spot welds on the vertical flanges and two or more on the lower flange. There is also a small flange at the very back of the inner rocker that is bent in towards the inside of the car that is spot welded on. You may be able to drill these out from inside the fender well.

I know how you feel about taking so long to do this job, I have replaced the inner and outer rockers on the driver and passenger sides. It took a long time , removing the old parts was the hardest thing to do. It wasn't easy but the finished product turned out real nice. Be patient and keep asking questions here and your results will fine. Good luck.

 

1) Could I have used lacquer thinner and done just as good a job?

Lacquer thinner does a great job of removing the bulk of the stuff that they put on the panels to keep them from rusting. I cleaned all my sheetmetal with lacquer thinnner, first wiping it down with a rag, then spraying it with a cleaning gun.

After that, I cleaned again with an oil and wax remover from PPG, DX330, followed by DX579 metal prep or Metal Ready applied with a scotchbrite pad. Then it's ready to shoot epoxy primer. I also used 3M weld-through primer along the plug welded edges.