I made a mold, using 2x4s, as Howard suggested. I put the 2x4s in the oven with the plastic sheets laying across it. With the oven at 325 degrees, it only took 3 or 4 minutes before the sheet was formed to the shape the lumber was setting on. Then I put the top of the mold over it to hold it in place. The first half was left in a little too long and started to warp along the edges, I took the second one out sooner and avoided the warping. I made some slices along the edge and used then reheated them to shape them into a 90-degree angle. So now I have the two halves.