To cover the layout or not ?

Flockburgh is situated quite near a huge NEC door this year at Warley. Worried that muck, dust and rain might blow in and damage things, we bought a 5 by 4 metre thin polythene sheet to cover the model up. In the erie sodium lighting, it looks quite spooky as the gossamer thin plastic billows around.

Is this a good idea though ? Normally we don't bother covering the model overnight at shows yet others go to great pains to do this. I can understand traders being keen - it's a security measure more then a hygiene one, but I've always felt that with layouts you stand more chance of damaging detail hauling sheets on and off the model.

The other thing is that there is likely to be more dirt around when the public are in than when the hall is empty. Therefore you'd be better off covering it when the filthy people are wandering around. At least that way they won't be able to see anything to complain about !

So, do you cover or not ? And why ?