I have a very similar arrangement to Peter with a Simmond's version of the 3 zip tonneau cover and I have found that it is on the car and in use most of the time but particularly in the colder months when I am driving on my own and like to keep the heat in the car.
It is also very useful to keep luggage and other items secure and out of sight behind the seats when travelling two up. The only downside is that mine is a fairly heavy mohair version and, if for any reason one wants to put the hood up after a downpour has soaked the cover, one then has to find somewhere to put it. Having said that, I still wouldn't be without it.
