Photo # 1. Chipboard is basically the heavy stock card board piece you find on the back of a yellow legal pad. You can buy it in bundles fairly cheaply. It can be bent dry for gentle corners and for sharper curves it can be wetted and shaped over a form, then dried with a heat gun. It will then retain this new curved shape.
Photo # 2. This shot shows the first layer of chip board formed and fitted into the corner. After making this corner I was not at all pleased with the shaped the curve was taking and the uneven surface that was produced.
Photo # 3. To try to make a more well rounded curve and a smoother working surface, I first attempted to cover the chipboard with some easier to form card stock. This did not improve things much and I was still quite unhappy with the surface and the overall strength and durability of the form.