It's a great concept and I hope it works in practice as well as you describe it.
I'd be concerned if your intention is to get the grades to fold over on themselves. Or are you planning to break down the rail lines in sections too? That's what I did for our 9 x 5 Christmas display this past year. You'll be dealing with a lot of different clearances; first to get the tracks to play well together running trains and then to get it to fold over on itself. Then when you go to open it up again you may discover though it closed up neatly the clearances are different in the opposite direction and the track is actually locked into itself when you attempt to open it up.
What I did with our display was break the track down into sections. We secured the track to a 5/32 plywood sub roadbed. Actually I used Fastrack on top of 3/8" closed cell foam, on top of the 3/8" plywood sub roadbed.
Our elevations rose from 7" to 21". The plywood roadbed was attached to the piers. I believe we broke the elevated sections into 7 pieces with the piers still attached. The table was broken down to two 4' X 5' sections and two 27" X 12" filler pieces leaving 6" X 12" space in the middle of the table to allow a easy pass through for electrical connections.
We only had to move the display in this manner twice; a block away each time. When it came time to store it away we took everything completely apart.
We use 1" x 2" grid work under all our display tables and never brake them down until they're larger than 8' x 4'. An easy way for one person to move them is by making cut outs on a 1" x 4" and attaching it with c clamps to the grid work. We also cover the table tops with moving blankets when we move them.
Maybe none of this information works for your situation but it never hurts to have a plan b or c in available just in case. Good luck Hope to see your successful creation down the road.
