Chip and scrape off all the rust that you possibly can. Treat with a rust remover/converter of your choice. Ensure you really have removed or converted all the rust then paint with a coating of your choice. I suggest that Hammerite will not stand up to the bashing these things get but then I dont know what will. A plastic coating such as Plasti Dip perhaps.
Getting rid of all the rust first will be the key to success.
Are these rings or loops for tying the anchor down? Galvanising would be the most robust - posters on here have suggested asking trailer manufacturer to put stuff in a batch for treatment. Rust doesn't look so bad on working boats but stained yacht decks are very unsightly aren't they. Maybe can replace with stainless.
A company called Frost provide paints etc for car restorers. They have a variety of rust removers as well. Free post too. Just got a brochure through last night, I will try them as Hammerite is no good.