Wire wheel and POR15. I have spent the last year POR15 my frame. Mastercoat makes good stuff as well, much cheaper than POR15, but not the same beast. Most paint shrinks as it dries, the moisture leaving the paint and leaves tiny holes where water can get through. POR15 does the opposite. goes on thin like fingernail polish and expands as it dries, making a perfect seal. No more rust ever again. A tiny can goes a LONG way. I did most of a frame rail with one tiny can. You can get 5 cans on Ebay for 50ish bucks IIRC. Ii still have 4 cans in my garage...lol.
I predict future happiness for Americans if they can prevent the government from wasting the labors of the people under the pretense of taking care of them.
Thomas Jefferson
96 Eclipse Spyder GSX (already turbo, AWD swap)
93 Eagle Summit AWD (4G63 turbo swaps)
I can second the POR15.
I used it on a trailer hitch I had on another vehicle years ago, and aside from a couple of spots that needed recoated later (I didn't clean the original surface well enough before the first coat) it worked very well.
Based on my experience, I'd suggest taking the hitch off so that any rusty spots can be cleaned properly with a wire wheel down to clean metal, then reinstalling it once the whole thing is properly coated and cured.