Thank you Kay.
I don't sell so I only frame for myself and when I do I simply put the paper in the frame and then put a panel board behind it. They sit nicely and I have yet to have one warp. The ones I like will go back between the covers of the pad they came in. I stand the pads horizontally against a wall in my painting room. To my amazement they do not warp.
I have had a few on the wall for a few years.