The cover shouldn't scratch / damage the paint, providing that the paint is clean and dry when you put the cover on. If there is dirt on the paint and the cover slides across the dirt, it could cause scratching.

Having said that, it's worth looking at the average humidity levels while the car isn't being used: if it's very high during the months you are away then it may be better to let the car get dusty without the cover on, so that moisture doesn't get trapped.

Thanks for the replies.

The car stays in Thailand where average temperature is around 30 deg and its pretty humid. Also our condo is less than 1km from the sea. Cars don't seem to rust though. Our villa in Spain is also close to the sea and I notice much more rust evident on old cars there... not sure why.

Anyway, I'll probably not use the cover. The dealer supposedly included a 'glass coating' as part of the deal and also additional rustproofing under the car (a kind of thin black wax - probably doesn't really need it).

I kept a spare car in our barn over winter a few years ago and covered it with a cheap cover to stop it getting covered with pine tree dust which blows in under the roof sheet joints, I looked under the cover after a few weeks and found the car was wringing wet with condensation so off it came.