I went to Tractor supply and bought a gallon of "rust killer"(about 20$) its in their paint section near the liquid nails and paint rollers erc... then i bought a garden pump sprayer (about 10$) loaded up the sprayer and soaked the entire underside of my truck. let it sit for about 3 days then sprayed about 20 cans of Dupli color truck bed coating underneath my truck, everywhere. ill try to get some pics for ya (seems the galleries got deleted when the site changed over)

one thing, if you use the rust killer stuff, i would suggest wearing a mask of some sort, a dust/ paint mask at the very least.