The stuff I use (PPC Phix corrosion treatment) comes in a spray bottle and I degrease the surface first and then spray it down. Let sit for 5-15 min (longer if there's more rust) keeping it wet. Then I take a red scotchbrite and scrub the surface and wipe it down with a damp cloth. Do this once more if a lot of rust and corrosion remains. When it's at a point I'm satisfied with, or if I just want to spray it on a panel to protect it, you then spray a light mist over the entire panel, let sit for a minute, then wipe down with a damp cloth. This final step is what leaves the zinc coating on the panel.
I'd then put SPI Epoxy on the panel. To prep the panel I'll scuff the zinc'd surface with a red scotch brite then degrease.