After reading this entire thread (and a few other, plus watching YT videos) here's the plan I'm getting on how to protect the inside and outside of the frame.
1. Buy or rent a horoscope type tool to visually inspect the inside of the frame.
2. Drill drainage holes into the low points of the frame.
3. Buy a drain auger, attach a small chain to the end and run it back & forth to help remove rust scale inside the frame.
3. Power wash the inside of the frame.
4. Use a flexible magnetic tool to pick up rust debris. Rinse, repeat, rinse, repeat, until magnet picks up all rust debris.
5. Use Eastwood internal frame coating.
6. Finish by Fluid Filming the inside of the frame (possible on a bi-annual basis).
For the exterior of the frame.
1. Grind off the rust, including removing the skid plate. (Plan on buying Black Magic Brake nutsert kit)
2. Coat with Rustoleum rust inhibitor.
3. Top coat with Rustoleum Advanced Protective satin black enamel.
4. Finish off by coating with Fluid Film (annual to bi-annual basis).
6. Complete by writing Stellantis a letter letting them know what a shitty job Jeep did by not rust proofing the TJs frame, and might as well include Jeeps stupidity in use torx bolts.
Good demo of how Eastwood 360 internal nozzle works. FF to 10:37.