You can treat the inside of your tubing
Jobst Brandt thought it was nonsense
https://yarchive.net/bike/frame_rust.html
but he also thought water bottles were nonsense
I've had several frames rust out, from the inside. It's a worthwhile step for bikes that are ridden and put away wet, especially salted snow or by the ocean, tourers, commuters. I wouldn't do it to a nice fair weather classic.
I use common hardware store LPS-3, or Fish Oil, not framesaver, cheaper. Also normally do it to a frame when it's stripped to avoid gunking up the bb or headset.
Waxing is good too but I actually think the internal treatment is more critical for a steel frame which is abused.