This is what I have done with no problems.
You can try to grind all the rust and thin the metal. You can chemically or blast all the rust - if you left any behind then you have wasted your time.
I convert it the best I can, then encapsulate it.
It will be fine until you are done with the truck.
I use my truck as a truck - hauling things. I also paid $400 for my truck.
Now if you are looking for a show truck then I am wrong. Sorry
It is your decision.