I have used illustration board for my acrylic paintings since 1983. But, I paint mainly with an airbrush, and being able to control the levels of transparency and colour intensity is the key to my work.
Since I paint only on hot press (smoothly calendared) illustration board, I've never needed to gesso my boards, nor seal them in any way.
I have just ordered some acid-free illustration board, and will be using only that from now on.
Synthetic Sky Studios
Science Fiction Fine Art