Depending on how thick your 2x4 plywood sheets are, and how skilled you are at woodworking, you could cut a groove into the long edges and join them with splines. Or you could simply build a frame of 1x4’s and screw the plywood sheets to it.
Gosh, I haven’t played with my trains in ages! My most recent efforts were in N gauge.
Evening Tweeze, Hugs.
Happy New Year to you and Mrs. Tweeze.
Were I any good, I would’ve figured something out years ago. But as long as I have the trains running, I’m fine. The boards will go in the basement behind the Christmas boxes. The planks will wind up in the garage where they may or may not survive until next year.