The cross piece
I wanted the cover to be collapsable. I decided that the best way to do this was to string two pieces of wood as spanning blocks between each arch with a piece of bungee cord running under tension through the middle. The idea is that it can be easily collapsed and straightened out. This section shows how I made the spanning blocks.
I needed to drill a hole through an eight inch piece of wood lengthwise. I wanted the hole to be fairly close to the center on both ends for this to work properly. Also the drill bit was too short to go all the way through. I set up this jig to center the bit in the piece of wood.
Here is the drilling in progress. I drilled half way through. Then I turned the block around and drilled from the other end. To finish I cleaned up the hole by taking the block out and drilling all the way through.
Here is the finished piece of wood with the hole in it. It is not perfect but it will work well enough. I made four of these.