Making a Painting Support Board (for Smaller Paintings)
This video shows how to make a lightweight waterproof board to support a small watercolor painting while you work. This method will not prevent buckling, but the paper will flatten out again after it dries.
This is only suitable for small sheets (up to 1/8th or 1/4th sheet depending on how wet you work). For larger paper, check out my video on how to stretch watercolor paper.