ben wrote:

Why not just pull it taut and put a couple of screws in at each end? It
might sag a bit over time, but will you see it?

It will actually be visible in this case - it's a storage shed.
But more importantly, it will be supported on battens screwed to
the rafters (sitting on top of the battens). If it was to sag
significantly, it would fall off the battens, hence the question.

I'm not sure screwing would be very successful, given the low
denisty nature of the material.

--
Grunff