I just took a look at my Six Moon Designs pack (2005 Comet, long since discontinued). It has flat stays. On each stay, the side towards my back has heavy nylon twill tape, stitched to the back of the pack on both sides. The inside is just the fabric used for the back and bottom of the pack, 420D pack cloth. I bought the pack in the the summer of 2006 and there are no signs of wear yet! I don't see why you couldn't use the same design for tubular stays. The width of the twill tape will, of course, depend on the size of the stays.
There's a review on BPL here, which has photos showing some of the stay detail:
I hope this helps!