I really don't think that moving anything away from the wall will keep bugs off the layout. They have six or eight (or more, if we're talking centipedes and the like) legs and no respect for gravity at all. Then there are the wings. Some of our modeling materials are
tasty to them, too, though less than in the past - they can love old paper and cardboard, but the pink and blue foam is not food.
Now, I'm going to give you the solution that absolutely works, and my layout proves it.
It is even in an outbuilding which, while very livable (in the hobby sense), is not even really airtight - or bugtight.
If you would like, cover your equipment with newspaper. I do this only casually and have seen no residue on anything. Set off a bug bomb in the layout area.
Do this twice a year - spring and late summer. Easy. Quick. Safe - just leave for 2 hours.
I live on the Gulf Coast with Major League bugs. No sissy Northern insects here. We have
cockroaches that turn and say to you "what you lookin' at?"
This works, in the house and the "train building". It's also cheap.