I am agreeing 100 percent. from coater to coater, that is the exact same thing I recommend!So to answer a few questions here, as this is what I do for a living.
A) The best course of action would be to stop in and see your local coater, have them chemically stripped, outgassed, blasted, zinc primed, and then top coated. If they are just something like 2" angle iron, expect to spend about $18/ft for this job. If you do it without the zinc (I wouldn't) it would land you roughly in the $12/ft area. If you choose a textured finish it will hide a lot of the pitting. Alternatively you could have the pitting welded up and smoothed out, then top coated for a perfect finish.
B) To the guy above, you definitely CAN blast powder off, you just need a pressure pot and a large volume of air to do this efficiently. I blast powder off with a 260cfm compressor and a pressure pot. Chemically stripping it easier and my preferred method.
C) Spray paint would be a pretty poor option as it will not last nor will it adhere well to the powder. You would be better off using something like a rubberized bed liner.