Aluminum or steel? My go-to is always epoxy primer followed wet-on-wet with whatever topcoat you want, but if I know you, you’re a little more “budget oriented”.
Lol
If that’s the case and you just want to spray bomb them, you really can’t go wrong with a decent etch primer followed up by any VHT product. Their Chassis and Roll bar paint, and their Caliper paint are both very robust. I wouldn’t clearcoat them as is, there probably isn’t enough tooth for it to stick without an etch primer, plus it’ll turn yellow with the heat over time.