How about buzzweld extreme chassis paint , just used it on the suspension bits and axles on my project .
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Galvanise them, then forget about it. Less hassle, might work out cheaper, will outlast the vehicle. No brainer really when you think about it. Chuck a few other bits into the tank as well if you need to make the weight up, win win.
Then you need an etch primer and some black paint, protection isnt your problem here, making the paint stick is, hence the etch primer. If you think the parts need more protection than the galv then you are wasting your time and your money.