[LT7A]

That's a very cool Blazer. Red, white top, wagon wheels. You need to wear I Ski mirrored sunglasses when you drive it. The ones with red white and blue frames, haha. Rust-Oleum has a product actually called rusty metal primer. POR 15 will certainly more than do the job, but the rusty metal primer with a top coat of the color of your choice should also do the trick. After all, it's not out in the elements. looking at the adhesive, I would expect that you may need to employ both approaches mentioned, along with a third one. I think you'll spend a lot of time with the wizzy wheel to get that stuff off so I'd recommend starting with heating it up and getting a plastic scraper. There are also plastic razor blades that are available at paint shops. They don't last a long time, but they do have a finer edge. I think you will need to do final clean up with a solvent, Goo Gone might do it. If not, mineral spirits with plenty of ventilation and/or a respirator. You can step up to brake cleaner and then carburetor cleaner if you need to.