away with the dust!
My HO layout is small....about 14' long by 4' deep. I buy the very thin plastic sheting sold in Home Depot designed to cover furniture while painting. It's so light weight it doesn't knock anything over, and trees are not damaged. Yes, it helps to glue down tall things like water towers, etc. After as little as two weeks I can see a dust layer. When it gets really dusty...I just shove the sheeting in a plastic bag and toss it. Total cost is about $2 for a new cover....cheaper if you wait for a sale.