I sandblasted some surface rust around my wheelwells and a few other places. I use silica sand and don't get too close with the nozzle. So what do I do next to ensure none of the rust is left behind and shows up years later? Do I sand and then use POR 15 or and etching primer or what? Any help would be greatly appreciated.

Is this on the body or under car? Under car POR15 is OK on the body epoxy etch prime

It's on the body. Quarter panels.

Thanks

Should I use a metal wash or anything else before the etching primer?

It's as clean as it's ever going to be after blasting so get it in prime as soon as possible. Don't touch it, sand it, or use any chemicals on it; just a good epoxy or self etching primer. I don't feel that PR15 or any of the so called "rust encapsulating" coatings should be used anywhere on a car. If the surface is properly cleaned and prepared, ordinary primer will work just as well and it will be totally compatible with top coats.

Tom

epoxy primer and only epoxy primer.