From what I remember about the highway code book, it only covers right hand drive vehicles. I can do all of those, not that anyone else on the road knows why I'm flapping my arms etc, but if the canvas is up, nobody would see any signals anyway.
If I simply reversed the signals for the left seat, they are still less likely to be seen. Following drivers sitting on the right of their vehicles, looking diagonally, still have their vision blocked by the canvas. My arms aren't long enough to stick out far enough!
Steve