agree with gordon that if you try scraping you'll be there forever & still miss some. The Chassis Saver paint is a 1-step convertor/encapsulator & topcoat that dries like epoxy or concrete. Once its on there, its not coming off and theres no issue with rust under the paint as it converts all the rust.
1) get the truck up on ramps and pressure-wash/blast off all the rust/sand/mud/salt/crud. Let dry. Just leave it there to dry, don't drive anywhere.
2) Wear coveralls or a painters suit, gloves &goggles/faceshield. DON'T LEAVE ANY skin exposed.
3)Paint on preferred 'paint'. I prefer CS over POR15 as POR is a 3 step (clean/prep/paint) system vs 1 step. I tried POR15 years ago on an old truck. didn't use their prep chems and had some spots that did not adhere. had to scrape & repaint those areas. I've not seen this happen with CS as long as you degrease.
Eastwood Company also has some good convertor/encapsulator 'paint'
Be sure when painting it on to get it on heavy. really brush it into any area with angles.
If you get CS or POR on your skin or hair, you'll be cutting your hair or waiting for your dead skin for a few weeks (like getting superglue on your fingertip but more obvious)
I need to do this. Dang California SALTed roads.
Can you tell me more about the 2 products listed. Assume that once you prevent oxygen from reaching the steel then no further rust will form.
both convert &encapsulate the rust/metal, sealing O2 from the metal.... no O2, no rust, even if it was present before