i find it is fine to paint on canvas board, but take care with the amount of moisture you allow to sit on the canvas; remember, it is on cardboard. i had let some rolled air dry clay sit on it over night covered by plastic and it caused it to warp. im sure that if you had it someway mounted onto your easel, maybe used a masonite board, and basic hand clamps (easy to move around as you work) you should'nt have a problem. if you're really worried about archival, then streched is probably the way to go. but these days they are also offering canvas already mounted on a masonite or clayboard, which is also sturdy.
i'll stop talking so much now :)) hope it was helpful :)