Ah! there is a post on that
here .
You fold in the corners of the tonneau in diagonally to make triangle on each side and in that way the seatbelts are reasonably free. I am also experimenting with a bungee cord stretched across the car behind the seats and hooked into the hood frame. In that way the tonneau can be supported by the cord and then dropped down behind the seats leaving the luggage space covered.
I have decided that the tonneau cover is best if the side screens are off but the hood cover is best when they are on.