It sucks, but all the rust paints and rust converter products over promise and under deliver.
I put myself through university working in an autobody shop and have restored several collector cars here in Canada, so I know about rust.
If you don't cut it out, it will come back. Sandblasting works, grinding works and replacing metal works. There is no paint that will stop rust. If you paint over rust, you have rusty metal with paint on top of the rust. sooner or later the rust will be back.
I've used Rustoleum, Tremclad and POR15 on my projects. POR15 lasted the longest, but the rust did come back.
Either sandblast your frame and repaint right away before it rusts again, or just paint it every few years.
1977 Safari Land Yacht
2005 Toyota Tundra SR5
2022 Toyota 4Runner SR5