Thanks for that. I think I am beginning to understand now. Most of my driving will be short trips of up to 100 miles or so, under virtually guaranteed blue sky, so I would want the tonneau cover.

For occasional longer trips, I would put the hood up some time in advance to avoid a last-minute panic if sudden heavy rain arrived.

It seems that the tonneau cover is a worthwhile optional extra for me, though perhaps it is more trouble than it's worth for those who drive in more changeable conditions.