Bought the tonneau from GD. And because each car shell is made individually, and, as the builder drill and fit the front air vents and the fixings for the soft-top frame behind the roll-hoops, the Tenax fasteners do not come as an integral [fitted] part of the tonneau.  So, as this is one of those jobs you can't mess up, I had a proper car upholsterer fitter put in the Tenax fasteners. 

Tenax Popping Tool

And here's a neat little tool I made to pop the Tenax.

One or two are sometimes a bit awkward to pop. A piece of hard plastic, shaped with the diameter of the inner bit.