Just a thought -- and maybe someone else who knows better can chime in -- but the metal used for petcocks is, of course, different from the tanks. In my experience, they have been susceptible to corrosion and I'd be worried about letting it sit in contact with vinegar for very long (although, of course, since it's turned off it's just the top part). I've seen quite a few 350F petcocks corroded beyond use over the years.
I've been babying a 350F tank for 5 or 6 weeks, stripping it (with the kind of weak stripper available here in CDMX, or at least what I found), then smoothing out a couple of dings with bondo (and taking my time -- several days). I had bought POR15 kits (I have another tank in the wings) and decided to go that route. Went through the three steps, got it bone dry, added the final sealant -- and it looks great. I used rubber stoppers to seal it off.
