i used coldpress watercolor paper right off the pad (strathmore, i believe). i plan the painting in pencil directly on the paper, then cover everything with matte medium (or gel medium, basically anything that's clear). after that i paint in oils.
to my understanding, there's no such thing as special anything when working with oils (panel, paper, wood, canvas, etc). oil will rot whatever surface you put it on if you don't first protect it.