Thanks for all the replies!! So much to learn..so little time!!
The vacuum with a nylon over the opening is a great idea, keep those loose parts out of the bag..lol, and I have a small can vac that the flow can be adjusted with a secondary opening on the nozzle handle.
I actually made a frame at one point to hold some plastic, but it was to bulky to move easily alone and there isn't enough head room in the basement to suspend it on pulleys.
Penn.....I WAS thinking of a hepa controlled room!! But your idea of sides on the platform is excellent! I've been thinking of backdrops anyway, and I could put the boards on the sides mounted on pins so they are removable for maintenence, the boards could have the backdrop scenery AND hold the plastic cover from touching any of the buildings!! I could remove only the front board to run the train.
Yup time to build a section of that and see how to support it and test for functionality!! Ooooo maybe hinges!! The whole table is set on a rolling frame I built to move it away from the wall while running or working on it, that would give room to fold down the sides and be easier than pins!!
Thanks everyone for your ideas...got me thinkin!!!