Any paint type coating will chip and flake. Herculiner is the most durable linerundercoat I've found but I still wouldn't put it under any of my trucks. You should go with oil - fluid film, bar and chain people use all sorts of stuff. This is what I've found to be the best, lifetime treatment with a single application for most areas underneath, A arms and diffs will need touch up every few years -
Ultimate oil undercoating guide (DIY Waxoyl)
The conversion products use and acid, usually phosphoric, one listed here uses gallic, however if you cover rust in oil it won't rust further making this step unnecessary
Linear Mode
