If you've built a baseboard with the thin battens shown in that clip, especially if it now has track fixed down. There is something you can do which will stiffen it up, but will increase its weight somewhat. Cut or have cut two approximately six inch wide strips from 6mm ply each 12mm longer than the board and two more the same length as the board's width. Screw and glue them to form a frame around the board. You can then fasten it either permanently with screws and glue or temporarily with a greater number of screws to the edges of the board. It's up to you whether you have the top flush with the surface the bottom flush with the bottom of the frame or something in between. If you want even more rigidity you can go for a central scenic background or a high level road down the centre hiding a similar stiffening beam.
I'm afraid if you want lightweight and portability you need to start with a different design. There are a number of designs to look. At all take the approach of multiple smaller boards locked together, two worth looking at are rigid insulation blocks edged with thin play and small upturned plywood trays with deep sides, There are more, it really depends on your abilities or depth of wallet.