Thankyou all. It seems that, on the whole, a cover is a good idea. This is my first new 'van and it will have to last, so I want to protect it the best I can. I did not have the opportunity to use my old one this year, and when I took it out of storeage it was in quite a state. I used to keep it at home and this wasn't so much of a problem, but I now use storeage that is only 1/4 mile away. There are no trees or indeed anything that overhangs the 'van, so a cover is just to protect it from the elements. It will get a good polish in any case.
I am aware of the possible problems with using cling film on the windows, perhaps an old blanket or sheet may be better?
I like the idea of the cardboard masks, I did not want to use the blinds for fear of them losing their tension, and not using the curtains will save them from fading.
Thanks
Gary