There are a number of these products on the market. I have used them for at least 30 years and found them to be good. However if your frame is rusted bad enough to make it unsafe, coating it with a rust converter won't make it any stronger. It does what is advertised. I had a 42ft fish boat and never would think of painting
any rusty steel surface without coating it with a rust converter first. It only works on rusted steel not new or where it was ground down clean.
The product I used was called Rust Not. there are others. In your case Canadian Tire or Lordco would have it.