Yeah if you have plastic tub of some kind with sufficient width you'll have a place to soak it. I've only removed a little rust that way. Getting it all won't happen with vinegar/baking soda in my experience. Gotta scrub or sand it too.
Also in my experience, it only takes a short while for the nickel plating to disappear, and then only frequent, greased use will stop rust from appearing. Just like with cast iron.
For grates that don't get regular use however, this is a problem. After cleaning yes, you'll want to coat with oil, spray oil is easiest, but you have to then worry about oil sitting on grates that potentially goes rancid.
Wish I had an answer/regimen for all this but the best thing that *seems* to work is to just leave them gummed up with food grease, then scrape off the top layer when the coals get them hot. Just like 1buckie shows above!