To keep watercolor paper from buckling while I'm painting I tape it down with masking tape to a "paint board" I made from the back board of a used up art paper pad which I covered with kitchen cupboard lining. The lining makes the masking tape easy to remove when I'm finished the painting, and the board is easy to wipe clean of any paint. Even acrylic paint comes off with a little stiff scrubbing.
It's simple to make, cut the lining a little bigger than the board on all sides so that you can overlap the edges, smooth it out and you're done! I've made several of them just in case I'm working on two watercolors at the same time. And I made a smaller one for my smaller paintings.
