I had Eric send me the sliders metalized and then powder coated them at a local place, it was $60 for me to have the both coated locally... you also don't have to worry about freight messing up the finish.
BTW... Zincnation can coat them with either zinc OR aluminum... You want zinc for paint... aluminum for powder coat (though I bet paint will stick ok too). I think his default is the aluminum, but specify what you plan to do with them when you order.
Eric is expanding his shop to add powder coating as an in-house coating option, but I HIGHLY recommend the Aluminum/Metalized coating. It will save them from rusting.
Here is a shot of the sliders in Black textured powder coat. I didn't get a shot of just the metailizing.. but ill add a picture of the bumper/skid shipment that had the same coating.. its white and rough, like 200 grit or so.