As promised, here are some pics of the webbing straps.
First, the original setup. Double D-rings, 3 down each side, fiddly to use and didn't really do much in terms of tensioning the cover.
I replaced them with the webbing straps and push type buckles that were going over the tent section:
Much quicker to use now
There is still at least a foot of strapping on each one after tightening them fully, so heaps of room to store more stuff under the cover if needs be. This setup also eliminates the billowing of the cover when on the road, hopefully reducing a bit of drag.
Matt