Rather than make my own baseboards, I decided to use Grainge and Hodder plywood kits, which make up into light, strong box sections. Two 1200 x 400mm units would be big enough for the shed, a point and a length of track, and still fit in the car.
As you can see, the first job is naming of parts. Laser-cutting means it all fits together fairly easily, with a bit of encouragement from a rubber mallet, size medium. Wood glue keeps the structure solid.