There’s a lot of debate on thermal screens, toppers etc. for your Cali. I chose this one because of price, convenience of fitting and simple logic; I wanted better thermal insulation up top. Works well, simple for me to fit even on my own and rolls up into a neat bag that can be easily stowed. Another big advantage that I have found is that you can put it up when you need it. i.e. if you are getting too cold and decide you want to add the screen in the middle of the night. I have even done so in a storm!
And how it is attached at the back. It’s put on starting at the back and working around the sides and front using a long handled broom to push into place. Bungie cord secures the two ends at the back. Green mini tarp is only if it’s very wet – otherwise there is a useful breather space at the back.