To do it properly I would get it sand blasted or even better dipped. There was a company I looked at that could then galvanize the shell as well, cant remember then name though.
Well it all depends on the extent of the surface rust, and also the extent to which it was bare metalled in the first place. Far too many variables.
If it was just the outer panels which were bare metalled, and they have lightly corroded, then it would be easy enough to buzz them back and apply a metal conditioner then etch prime. But remember, steel will start to corrode immediately, even if you can't see it. So all this needs to be done in succession to avoid the rust reforming.
If it were previously dipped or blasted, and the rust has come back all in the cavities etc then there is not much other choice than to have it re dipped/blasted.
Dipping and blasting both have their place, but unless it is needed and you have a plan for when you get it back, then it can make matters worse.
Dipping will create areas where rusts will form where it may never have been before. unless you are 100% sure you have coated it with primer/cavity wax. Also I've seen cars come back where the acid has not fully drained from seems and cavities etc causing more problems.
Of course the ideal situation would be to have it dipped, returned for any repair work, re dipped and then e-coated.
Blasting is good if it's just outer corrosion that is a problem. But again, creates problems. Although not a massive problem, you'll just be left with piles of grit on the workshop floor every time you work on it as it vibrates out of the drain holes. And even when you're sure it's all out, you can be sure it will find some whilst painting and spoil the finish somewhere!