I wasn't thinking bare metal as the "goal" necessarily, more thinking that might be where at least some of it goes since I don't know what's under the paint.
True story about one painting experience: we live in a rental, and the previous tenants were using our place as a grow house. The DEA raided it and everything! When I painted my floorpans, I cooked up a supplied air system using a Tyvek suit and shop-vac (it totally worked), and can only imagine what my neighbors were thinking. No one said anything, but I probably don't need to push my luck! That was two years ago, though, so I think I could get away with priming, as long as it's a one-time quick-enough job.