Any self-etching primer will do.
Since this is for sliders, use a cheap paint, and one that's easy to get. You'll be touching it up lots. I've had good results with the "rubberized rocker guard" paint stuff from Ukranian tire. It's cheap, has a texture kinda like bedliner, and is easy to touch up. Hit the gouged area with a wire wheel and the shoot a touch up on top of it. I've done my diff covers, front skid plate, and rear bumper with the stuff. Because it's got a flex agent in it, it doesn't seem to chip as bad as other paints when the grit from the road hits it.