I'm currently using one of Lidl's full covers on a 75. Been on continuously for about 6 months now and it's staying together well.
The sun has faded it a little, but not really worried about that. I have put some large soft cloths over the bonnet, boot and roof before fitting the cover though, just to stop any chance of it marking if condensation gets under and metre wide bubble wrap (cable tied to door handles, etc) around the body perimeter to prevent any chaffing from wind.
But as covers go, it's pretty good, think it was under £15 ???
Would give it 9/10