Well, the best way is to carefully select the tip and understand what material is used. Most tips you see are chromed carbon steel. And the chrome isn't a nice triple chrome material, either. So expect road grime to discolor it and to chip it, promoting rust.
I have a set of brushed aluminum tips and they come clean every time...because aluminum won't rust. They clean right up and a little 3M ScotchBrite pad work now and then keeps them looking good.
You could try some rattle can clear coat to protect the tips. Not really sure how well it would work.