Unfortunately you can't hide rust. You may slow it down by sealing it under something but it will keep growing and eating metal causing failure of the materials on top of it. Rust "converters" are typically only surface deep and the chemicals don't play nice with the next layers on top. They falsely make you think you've killed the rust unless it's very, very minor. But if the rust is that minor, sand it off.
You basically have three options if you are trying to make a permanent rust repair - 1) Mechanically remove the rust - grind, blast, wirewheel, etc or 2) Cut out and replace all the rusted metal or 3) Professional Chemical Dipping (very hard to find these days and trapped chemicals can leach out later causing problems). In any case, you must remove the rust, not hide it.
Not what you were hoping to hear, but media blasting is the likely the best way of doing a thorough job. It's so easy and gives you such nice clean metal with good tooth to work with. Grinding and wirewheeling is the next best option but easier to miss rust and remove excess metal. Any of it needs to be done with care to prevent adding new damage...
