I paint primarily with airbrush, and have only ever used illustration board, after a few less than satisfactory attempts at airbrushing on drawing paper with watercolours, before I had a clue what I was doing.
I recently switched to a 100 percent acid-free illustration board surface, and have yet to complete a painting using the new board, so I'm not sure how it's going to work out.
Illustration board is basically a piece of high quality drawing paper (textured or smooth) bonded to a cardboard (or, in the case of the acid free boards, rag) support.
I have never gessoed my boards, preferring the glass-like smoothness that the hot-press boards are manufactured with.
All my completed paintings are archival matted, and framed behind glass.
Synthetic Sky Studios
Science Fiction Fine Art